Source : Webster's Revised Unabridged Dictionary (1913)

Least \Least\, a. [OE. last, lest, AS. l?sast, l?sest, superl.
   of l?ssa less. See {Less}, a.] [Used as the superlative of
   little.]
   Smallest, either in size or degree; shortest; lowest; most
   unimportant; as, the least insect; the least mercy; the least
   space.

   Note: Least is often used with the, as if a noun.

               I am the least of the apostles.    --1 Cor. xv.
                                                  9.

   {At least}, or {At the least}, at the least estimate,
      consideration, chance, etc.; hence, at any rate; at all
      events; even. See {However}.

            He who tempts, though in vain, at least asperses The
            tempted with dishonor.                --Milton.

            Upon the mast they saw a young man, at least if he
            were a man, who sat as on horseback.  --Sir P.
                                                  Sidney.
      

   {In least}, or {In the least}, in the least degree, manner,
      etc. ``He that is unjust in the least is unjust also in
      much.'' --Luke xvi. 10.

   {Least squares} (Math.), a method of deducing from a number
      of carefully made yet slightly discordant observations of
      a phenomenon the most probable values of the unknown
      quantities.

   Note: It takes as its fundamental principle that the most
         probable values are those which make the sum of the
         squares of the residual errors of the observation a
         minimum.

At \At\, prep. [AS. [ae]t; akin to OHG. az, Goth., OS., & Icel.
   at, Sw. [*a]t, Dan. & L. ad.]
   Primarily, this word expresses the relations of presence,
   nearness in place or time, or direction toward; as, at the
   ninth hour; at the house; to aim at a mark. It is less
   definite than in or on; at the house may be in or near the
   house. From this original import are derived all the various
   uses of at. It expresses: 

   1. A relation of proximity to, or of presence in or on,
      something; as, at the door; at your shop; at home; at
      school; at hand; at sea and on land.

   2. The relation of some state or condition; as, at war; at
      peace; at ease; at your service; at fault; at liberty; at
      risk; at disadvantage.

   3. The relation of some employment or action; occupied with;
      as, at engraving; at husbandry; at play; at work; at meat
      (eating); except at puns.

   4. The relation of a point or position in a series, or of
      degree, rate, or value; as, with the thermometer at
      80[deg]; goods sold at a cheap price; a country estimated
      at 10,000 square miles; life is short at the longest.

   5. The relations of time, age, or order; as, at ten o'clock;
      at twenty-one; at once; at first.

   6. The relations of source, occasion, reason, consequence, or
      effect; as, at the sight; at this news; merry at anything;
      at this declaration; at his command; to demand, require,
      receive, deserve, endure at your hands.

   7. Relation of direction toward an object or end; as, look at
      it; to point at one; to aim at a mark; to throw, strike,
      shoot, wink, mock, laugh at any one.

   {At all}, {At home}, {At large}, {At last}, {At length}, {At
   once}, etc. See under {All}, {Home}, {Large}, {Last} (phrase
      and syn.), {Length}, {Once}, etc.

   {At it}, busily or actively engaged.

   {At least}. See {Least} and {However}.

   {At one}. See {At one}, in the Vocabulary.

   Syn: {In}, {At}.

   Usage: When reference to the interior of any place is made
          prominent in is used. It is used before the names of
          countries and cities (esp. large cities); as, we live
          in America, in New York, in the South. At is commonly
          employed before names of houses, institutions,
          villages, and small places; as, Milton was educated at
          Christ's College; money taken in at the Customhouse; I
          saw him at the jeweler's; we live at Beachville. At
          may be used before the name of a city when it is
          regarded as a mere point of locality. ``An English
          king was crowned at Paris.'' --Macaulay. ``Jean
          Jacques Rousseau was born at Geneva, June, 28, 1712.''
          --J. Morley. In regard to time, we say at the hour, on
          the day, in the year; as, at 9 o'clock, on the morning
          of July 5th, in the year 1775.

Source : WordNet®

at least
     adv 1: if nothing else (`leastwise' is informal and `leastways' is
            colloquial); "at least he survived"; "they felt--at
            any rate Jim felt--relieved though still wary"; "the
            influence of economists--or at any rate of
            economics--is far-reaching" [syn: {leastways}, {leastwise},
             {at any rate}]
     2: not less than; "at least two hours studying the manual"; "a
        tumor at least as big as an orange" [syn: {at the least}]
        [ant: {at most}, {at most}]