Source : Webster's Revised Unabridged Dictionary (1913)

Explain \Ex*plain"\, v. t. [imp. & p. p. {Explained}; p. pr. &
   vb. n. {Explaining}.] [L. explandare to flatten, spread out,
   explain; ex out+plandare to make level or plain, planus
   plain: cf. OF. esplaner, explaner. See {Plain},a., and cf.
   {Esplanade}.]
   1. To flatten; to spread out; to unfold; to expand. [Obs.]

            The horse-chestnut is . . . ready to explain its
            leaf.                                 --Evelyn.

   2. To make plain, manifest, or intelligible; to clear of
      obscurity; to expound; to unfold and illustrate the
      meaning of; as, to explain a chapter of the Bible.

            Commentators to explain the difficult passages to
            you.                                  --Gay.

   {To explain away}, to get rid of by explanation. ``Those
      explain the meaning quite away.'' --Pope.

   Syn: To expound; interpret; elucidate; clear up.

Explain \Ex*plain"\, v. i.
   To give an explanation.

Source : WordNet®

explain
     v 1: make palin and comprehensible; "He explained the laws of
          physics to his students" [syn: {explicate}]
     2: define; "The committe explained their plan for fund-raising
        to the Dean"
     3: serve as a reason or cause or justification of; "Your need
        to sleep late does not excuse your late arrival at work";
        "Her recent divorce amy explain her reluctance to date
        again" [syn: {excuse}]