Source : Webster's Revised Unabridged Dictionary (1913)

By \By\ (b[imac]), prep. [OE. bi, AS. b[=i], big, near to, by,
   of, from, after, according to; akin to OS. & OFries. bi, be,
   D. bij, OHG. b[=i], G. bei, Goth. bi, and perh. Gr. 'amfi`.
   E. prefix be- is orig. the same word. [root]203. See pref.
   {Be-}.]
   1. In the neighborhood of; near or next to; not far from;
      close to; along with; as, come and sit by me. [1913
      Webster]

            By foundation or by shady rivulet He sought them
            both.                                 --Milton.

   2. On; along; in traversing. Compare 5.

            Long labors both by sea and land he bore. --Dryden.

            By land, by water, they renew the charge. --Pope.

   3. Near to, while passing; hence, from one to the other side
      of; past; as, to go by a church.

   4. Used in specifying adjacent dimensions; as, a cabin twenty
      feet by forty.

   5. Against. [Obs.] --Tyndale [1. Cor. iv. 4].

   6. With, as means, way, process, etc.; through means of; with
      aid of; through; through the act or agency of; as, a city
      is destroyed by fire; profit is made by commerce; to take
      by force.

   Note: To the meaning of by, as denoting means or agency,
         belong, more or less closely, most of the following
         uses of the word:
      (a) It points out the author and producer; as,
          ``Waverley'', a novel by Sir W.Scott; a statue by
          Canova; a sonata by Beethoven.
      (b) In an oath or adjuration, it indicates the being or
          thing appealed to as sanction; as, I affirm to you by
          all that is sacred; he swears by his faith as a
          Christian; no, by Heaven.
      (c) According to; by direction, authority, or example of;
          after; -- in such phrases as, it appears by his
          account; ten o'clock by my watch; to live by rule; a
          model to build by.
      (d) At the rate of; according to the ratio or proportion
          of; in the measure or quantity of; as, to sell cloth
          by the yard, milk by the quart, eggs by the dozen,
          meat by the pound; to board by the year.
      (e) In comparison, it denotes the measure of excess or
          deficiency; when anything is increased or diminished,
          it indicates the measure of increase or diminution;
          as, larger by a half; older by five years; to lessen
          by a third.
      (f) It expresses continuance or duration; during the
          course of; within the period of; as, by day, by night.
      (g) As soon as; not later than; near or at; -- used in
          expressions of time; as, by this time the sun had
          risen; he will be here by two o'clock.

   Note: In boxing the compass, by indicates a pint nearer to,
         or towards, the next cardinal point; as, north by east,
         i.e., a point towards the east from the north;
         northeast by east, i.e., on point nearer the east than
         northeast is.

   Note: With is used instead of by before the instrument with
         which anything is done; as, to beat one with a stick;
         the board was fastened by the carpenter with nails. But
         there are many words which may be regarded as means or
         processes, or, figuratively, as instruments; and
         whether with or by shall be used with them is a matter
         of arbitrary, and often, of unsettled usage; as, to a
         reduce a town by famine; to consume stubble with fire;
         he gained his purpose by flattery; he entertained them
         with a story; he distressed us with or by a recital of
         his sufferings. see {With}.

   {By all means}, most assuredly; without fail; certainly.

   {By and by}.
      (a) Close together (of place). [Obs.] ``Two yonge knightes
          liggyng [lying] by and by.'' --Chaucer.
      (b) Immediately; at once. [Obs.] ``When . . . persecution
          ariseth because of the word, by and by he is
          offended.'' --Matt. xiii. 21.
      (c) Presently; pretty soon; before long.

   Note: In this phrase, by seems to be used in the sense of
         nearness in time, and to be repeated for the sake of
         emphasis, and thus to be equivalent to ``soon, and
         soon,'' that is instantly; hence, -- less emphatically,
         -- pretty soon, presently.

   {By one's self}, with only one's self near; alone; solitary.

   {By the bye}. See under {Bye}.

   {By the head} (Naut.), having the bows lower than the stern;
      -- said of a vessel when her head is lower in the water
      than her stern. If her stern is lower, she is by the
      stern.

   {By the lee}, the situation of a vessel, going free, when she
      has fallen off so much as to bring the wind round her
      stern, and to take her sails aback on the other side.

   {By the run}, to let go by the run, to let go altogether,
      instead of slacking off.

   {By the way}, by the bye; -- used to introduce an incidental
      or secondary remark or subject. 

   {Day by day}, {One by one}, {Piece by piece}, etc., each day,
      each one, each piece, etc., by itself singly or
      separately; each severally.

   {To come by}, to get possession of; to obtain.

   {To do by}, to treat, to behave toward.

   {To set by}, to value, to esteem.

   {To stand by}, to aid, to support.

   Note: The common phrase good-by is equivalent to farewell,
         and would be better written good-bye, as it is a
         corruption of God be with you (b'w'ye).

Mean \Mean\, n.
   1. That which is mean, or intermediate, between two extremes
      of place, time, or number; the middle point or place;
      middle rate or degree; mediocrity; medium; absence of
      extremes or excess; moderation; measure.

            But to speak in a mean, the virtue of prosperity is
            temperance; the virtue of adversity is fortitude.
                                                  --Bacon.

            There is a mean in all things.        --Dryden.

            The extremes we have mentioned, between which the
            wellinstracted Christian holds the mean, are
            correlatives.                         --I. Taylor.

   2. (Math.) A quantity having an intermediate value between
      several others, from which it is derived, and of which it
      expresses the resultant value; usually, unless otherwise
      specified, it is the simple average, formed by adding the
      quantities together and dividing by their number, which is
      called an arithmetical mean. A geometrical mean is the
      square root of the product of the quantities.

   3. That through which, or by the help of which, an end is
      attained; something tending to an object desired;
      intermediate agency or measure; necessary condition or
      coagent; instrument.

            Their virtuous conversation was a mean to work the
            conversion of the heathen to Christ.  --Hooker.

            You may be able, by this mean, to review your own
            scientific acquirements.              --Coleridge.

            Philosophical doubt is not an end, but a mean. --Sir
                                                  W. Hamilton.

   Note: In this sense the word is usually employed in the
         plural form means, and often with a singular attribute
         or predicate, as if a singular noun.

               By this means he had them more at vantage.
                                                  --Bacon.

               What other means is left unto us.  --Shak.

   4. pl. Hence: Resources; property, revenue, or the like,
      considered as the condition of easy livelihood, or an
      instrumentality at command for effecting any purpose;
      disposable force or substance.

            Your means are very slender, and your waste is
            great.                                --Shak.

   5. (Mus.) A part, whether alto or tenor, intermediate between
      the soprano and base; a middle part. [Obs.]

            The mean is drowned with your unruly base. --Shak.

   6. Meantime; meanwhile. [Obs.] --Spenser.

   7. A mediator; a go-between. [Obs.] --Piers Plowman.

            He wooeth her by means and by brokage. --Chaucer.

   {By all means}, certainly; without fail; as, go, by all
      means.

   {By any means}, in any way; possibly; at all.

            If by any means I might attain to the resurrection
            of the dead.                          --Phil. iii.
                                                  ll.
      

   {By no means}, or {By no manner of means}, not at all;
      certainly not; not in any degree.

            The wine on this side of the lake is by no means so
            good as that on the other.            --Addison.

Source : WordNet®

by all means
     adv : definitely or certainly; "Visit us by all means" [ant: {by
           no means}]