The Collaborative International Dictionary of English v.0.48:

Tell \Tell\ (t[e^]l), v. t. [imp. & p. p. Told (t[=o]ld); p.
   pr. & vb. n. Telling.] [AS. tellan, from talu tale, number,
   speech; akin to D. tellen to count, G. z[aum]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.
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            He telleth the number of the stars.   --Ps. cxlvii.
                                                  4.
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            Tell the joints of the body.          --Jer. Taylor.
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   2. To utter or recite in detail; to give an account of; to
      narrate.
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            Of which I shall tell all the array.  --Chaucer.
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            And not a man appears to tell their fate. --Pope.
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   3. To make known; to publish; to disclose; to divulge.
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            Why didst thou not tell me that she was thy wife?
                                                  --Gen. xii.
                                                  18.
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   4. To give instruction to; to make report to; to acquaint; to
      teach; to inform.
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            A secret pilgrimage,
            That you to-day promised to tell me of? --Shak.
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   5. To order; to request; to command.
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            He told her not to be frightened.     --Dickens.
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   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.
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   7. To make account of; to regard; to reckon; to value; to
      estimate. [Obs.]
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            I ne told no dainity of her love.     --Chaucer.
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   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.
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   To tell off, to count; to divide. --Sir W. Scott.
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   Syn: To communicate; impart; reveal; disclose; inform;
        acquaint; report; repeat; rehearse; recite.
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The Collaborative International Dictionary of English v.0.48:

Telling \Tell"ing\, a.
   Operating with great effect; effective; as, a telling speech.
   -- Tell"ing*ly, adv.
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WordNet (r) 3.0 (2006):

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, telling, telltale(a)]
    2: powerfully persuasive; "a cogent argument"; "a telling
       presentation"; "a weighty argument" [syn: cogent,
       telling, 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, telling,
         recounting]
    2: informing by words [syn: telling, apprisal,
       notification]
    3: disclosing information or giving evidence about another [syn:
       tattle, singing, telling]

Moby Thesaurus II by Grady Ward, 1.0:

219 Moby Thesaurus words for "telling":
   absolute, accounting, acid, adducible, admissible, agitating,
   announcement, armipotent, attestative, attestive, authentic,
   authoritative, based on, biting, breathtaking, celebrated, census,
   certain, charged, charismatic, charming, circumstantial,
   cliff-hanging, cogent, conclusive, consequential, considerable,
   conspicuous, conveyance, convincing, corrosive, counting,
   cumulative, cutting, dactylonomy, damning, decisive, determinative,
   disclosure, disquieting, distinguished, distracting, disturbing,
   documentary, documented, driving, dynamic, effective, effectual,
   efficacious, electric, eminent, enchanting, energetic, enumeration,
   esteemed, estimable, evidential, evidentiary, ex parte,
   exceptional, exciting, exhilarating, extraordinary, eye-witness,
   factual, final, firsthand, foliation, forceful, forcible,
   founded on, galvanic, giving, grounded on, gutsy, heady, hearsay,
   heart-expanding, heart-stirring, heart-swelling, heart-thrilling,
   high-potency, high-powered, high-pressure, high-tension,
   impartation, imparting, impartment, imperative, implicit,
   important, impressive, in force, in power, incisive,
   incontrovertible, indicative, indisputable, inflammatory,
   influential, intoxicating, inventorying, irrefutable, irresistible,
   jarring, jolting, maddening, magnetic, marked, material,
   measurement, memorable, mighty, mighty in battle, mind-blowing,
   momentous, mordant, moving, narration, narrative, nervous, noble,
   notable, noteworthy, notification, numbering, numeration,
   nuncupative, of mark, operative, outstanding, overcoming,
   overmastering, overpowering, overwhelming, pagination, penetrating,
   personable, persuasive, perturbing, piercing, piquant, poignant,
   potent, powerful, prepotent, prestigious, presumptive, probative,
   prominent, provocative, provoking, publication, puissant, punchy,
   quantification, quantization, rare, ravishing, recital, recountal,
   recounting, rehearsal, relation, reliable, remarkable,
   rememberable, reputable, retelling, review, ruling, salient,
   satisfactory, satisfying, sensational, sharing, signal,
   significant, sinewed, sinewy, slashing, solid, soul-stirring,
   sound, special, spirit-stirring, stimulating, stimulative,
   stirring, striking, strong, suasive, substantial, suggestive, sure,
   suspenseful, suspensive, symptomatic, tale-telling, tallying,
   tantalizing, thrilling, thrilly, transfer, transference,
   transmission, transmittal, trenchant, troubling, unforgettable,
   unsettling, upsetting, valid, vigorous, vital, weighty, winning,
   yarn spinning