The Collaborative International Dictionary of English v.0.48:

wiretap \wiretap\ n.
   the act or event of tapping a telephone or telegraph line to
   get information surreptitiously.
   [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

wiretap \wiretap\ v. t.
   to tap[5] (a telephone or telegraph line) to get information
   surreptitiously; also, to obtain or record (information) by
   use of a wiretap.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

wiretap
    n 1: the act of tapping a telephone or telegraph line to get
         information [syn: wiretap, tap]
    v 1: tap a telephone or telegraph wire to get information; "The
         FBI was tapping the phone line of the suspected spy"; "Is
         this hotel room bugged?" [syn: wiretap, tap,
         intercept, bug]