to tell on

from The Collaborative International Dictionary of English v.0.48
Tell \Tell\, v. i.
   1. To give an account; to make report.
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            That I may publish with the voice of thankgiving,
            and tell of all thy wondrous works.   --Ps. xxvi. 7.
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   2. To take effect; to produce a marked effect; as, every shot
      tells; every expression tells.
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   {To tell of}.
      (a) To speak of; to mention; to narrate or describe.
      (b) To inform against; to disclose some fault of.

   {To tell on}, to inform against. [Archaic & Colloq.]
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            Lest they should tell on us, saying, So did David.
                                                  --1 Sam.
                                                  xxvii. 11.
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