Source : Webster's Revised Unabridged Dictionary (1913)

Tongue-tied \Tongue"-tied`\, a.
   1. Destitute of the power of distinct articulation; having an
      impediment in the speech, esp. when caused by a short
      fr[ae]num.

   2. Unable to speak freely, from whatever cause.

            Love, therefore, and tongue-tied simplicity. --Shak.

Source : WordNet®

tongue-tied
     adj : unable to express yourself clearly or fluently; "felt
           tongue-tied with embarrassment"; "incoherent with
           grief" [syn: {incoherent}]