Source : Webster's Revised Unabridged Dictionary (1913)

Tell \Tell\, v. t. [imp. & p. p. {Told}; p. pr. & vb. n.
   {Telling}.] [AS. tellan, from talu tale, number, speech; akin
   to D. tellen to count, G. z["a]hlen, OHG. zellen to count,
   tell, say, Icel. telja, Dan. tale to speak, t[ae]lle to
   count. See {Tale} that which is told.]
   1. To mention one by one, or piece by piece; to recount; to
      enumerate; to reckon; to number; to count; as, to tell
      money. ``An heap of coin he told.'' --Spenser.

            He telleth the number of the stars.   --Ps. cxlvii.
                                                  4.

            Tell the joints of the body.          --Jer. Taylor.

   2. To utter or recite in detail; to give an account of; to
      narrate.

            Of which I shall tell all the array.  --Chaucer.

            And not a man appears to tell their fate. --Pope.

   3. To make known; to publish; to disclose; to divulge.

            Why didst thou not tell me that she was thy wife?
                                                  --Gen. xii.
                                                  18.

   4. To give instruction to; to make report to; to acquaint; to
      teach; to inform.

            A secret pilgrimage, That you to-day promised to
            tell me of?                           --Shak.

   5. To order; to request; to command.

            He told her not to be frightened.     --Dickens.

   6. To discern so as to report; to ascertain by observing; to
      find out; to discover; as, I can not tell where one color
      ends and the other begins.

   7. To make account of; to regard; to reckon; to value; to
      estimate. [Obs.]

            I ne told no dainity of her love.     --Chaucer.

   Note: Tell, though equivalent in some respect to speak and
         say, has not always the same application. We say, to
         tell truth or falsehood, to tell a number, to tell the
         reasons, to tell something or nothing; but we never
         say, to tell a speech, discourse, or oration, or to
         tell an argument or a lesson. It is much used in
         commands; as, tell me the whole story; tell me all you
         know.

   {To tell off}, to count; to divide. --Sir W. Scott.

   Syn: To communicate; impart; reveal; disclose; inform;
        acquaint; report; repeat; rehearse; recite.

Telling \Tell"ing\, a.
   Operating with great effect; effective; as, a telling speech.
   -- {Tell"ing*ly}, adv.

Source : WordNet®

telling
     adj 1: disclosing unintentionally; "a telling smile"; "a telltale
            panel of lights"; "a telltale patch of oil on the
            water marked where the boat went down" [syn: {revealing},
             {telltale(a)}]
     2: powerfully persuasive; "a cogent argument"; "a telling
        presentation"; "a weighty argument" [syn: {cogent}, {weighty}]
     3: producing a strong effect; "gave an impressive performance
        as Othello"; "a telling gesture" [syn: {impressive}]

telling
     n 1: an act of narration; "he was the hero according to his own
          relation"; "his endless recounting of the incident
          eventually became unbearable" [syn: {relation}, {recounting}]
     2: informing by words [syn: {apprisal}, {notification}]
     3: disclosing information or giving evidence about another
        [syn: {tattle}, {singing}]