means To make something known by speech or signs — or, in poker and beyond, a small unconscious signal that reveals what someone is hiding.

from From Old English 'tellan,' which meant to count, reckon, or recount — the same impulse that gives us 'teller' at a bank and the act of 'telling' a story. It's a cousin of 'tale' and shares roots with German 'zählen' (to count) and 'erzählen' (to narrate), because once upon a time, to tell a tale was literally to tally it up, item by item. The poker sense — the 'tell' as a betraying twitch — is a much later spin, where what your body counts out, your face would rather not number.