Source : Webster's Revised Unabridged Dictionary (1913)

Then \Then\, conj.
   1. Than. [Obs.] --Spenser.

   2. In that case; in consequence; as a consequence; therefore;
      for this reason.

            If all this be so, then man has a natural freedom.
                                                  --Locke.

            Now, then, be all thy weighty cares away. --Dryden.

   Syn: Therefore.

   Usage: {Then}, {Therefore}. Both these words are used in
          reasoning; but therefore takes the lead, while then is
          rather subordinate or incidental. Therefore states
          reasons and draws inferences in form; then, to a great
          extent, takes the point as proved, and passes on to
          the general conclusion. ``Therefore being justified by
          faith, we have peace with God.'' --Rom. v. 1. ``So
          then faith cometh by hearing, and hearing by the word
          of God.'' --Rom. x. 17.

Then \Then\ ([th][e^]n), adv. [Originally the same word as than.
   See {Than}.]
   1. At that time (referring to a time specified, either past
      or future).

            And the Canaanite was then in the land. --Gen. xii.
                                                  6.

            Now I know in part; but then shall I know even as
            also I am known.                      --1 Cor. xiii.
                                                  12.

   2. Soon afterward, or immediately; next; afterward.

            First be reconciled to thy brother, and then come
            and offer thy gift.                   --Matt. v. 24.

   3. At another time; later; again.

            One while the master is not aware of what is done,
            and then in other cases it may fall out to be own
            act.                                  --L'Estrange.

   {By then}.
      (a) By that time.
      (b) By the time that. [Obs.]

                But that opinion, I trust, by then this
                following argument hath been well read, will be
                left for one of the mysteries of an indulgent
                Antichrist.                       --Milton.

   {Now and then}. See under {Now}, adv.

   {Till then}, until that time; until the time mentioned.
      --Milton.

   Note: Then is often used elliptically, like an adjective, for
         then existing; as, the then administration.

Source : WordNet®

then
     adj : at a specific prior time; "the then president" [syn: {then(a)}]

then
     n : that time; that moment; "we will arrive before then"; "we
         were friends from then on"
     adv 1: subsequently or soon afterward (often used as sentence
            connectors); "then he left"; "go left first, then
            right"; "first came lightning, then thunder"; "we
            watched the late movie and then went to bed"; "and so
            home and to bed" [syn: {so}, {and so}, {and then}]
     2: in that case or as a consequence; "if he didn't take it,
        then who did?"; "keep it then if you want to"; "the case,
        then, is closed"; "you've made up your mind then?"; "then
        you'll be rich"
     3: at that time; "I was young then"; "prices were lower back
        then"; "science as it was then taught"