WordNet (r) 3.0 (2006):

tell on
    v 1: give away information about somebody; "He told on his
         classmate who had cheated on the exam" [syn: denounce,
         tell on, betray, give away, rat, grass, shit,
         shop, snitch, stag]
    2: produce an effect or strain on somebody; "Each step told on
       his tired legs"

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "tell on":
   babble, be indiscreet, be unguarded, bear witness against, betray,
   betray a confidence, blab, blabber, blow the whistle, blurt,
   blurt out, fink, give away, inform, inform against, inform on,
   leak, let drop, let fall, let slip, narc, peach, rat,
   reveal a secret, sell out, sing, snitch, snitch on, spill,
   spill the beans, squeal, stool, talk, tattle, tattle on,
   tell secrets, tell tales, testify against, turn informer