telling

Etymology 1

verb

1. present participle and gerund of tell

adj

1. Having force, or having a marked effect; weighty, effective.
   a telling blow
2. Revealing information; bearing significance.
   a telling smile
   But ever since the concept of "hamartia" recurred through Aristotle's Poetics, in an attempt to describe man's ingrained iniquity, our impulse has been to identify a telling defect in those brought suddenly and dramatically low. 21 October 2014, Oliver Brown, “Oscar Pistorius jailed for five years – sport afforded no protection against his tragic fallibilities: Bladerunner's punishment for killing Reeva Steenkamp is but a frippery when set against the burden that her bereft parents, June and Barry, must carry [print version: No room for sentimentality in this tragedy, 13 September 2014, p. S22]”, in The Daily Telegraph (Sport)
3. Serving to convince.
   telling evidence

Etymology 2

Gerund from the verb tell, from tell + -ing.

noun

1. The act of narration.
2. The disclosure of information.
3. (archaic) Counting, numbering.
4. (chiefly in the negative) Ability to determine.
   "One white man." said Bill, after a brief inspection. "Out on his line, I s'pose, and there's no tellin' when he'll be back. So we won't wait. We'll just serve notice on him." 1922, A[rthur] M[urray] Chisholm, A Thousand a Plate