The Collaborative International Dictionary of English v.0.48:

Encroach \En*croach"\, v. i. [imp. & p. p. Encroached; p. pr.
   & vb. n. Encroaching.] [OF. encrochier to perch, prop., to
   hook, fasten a hook (perh. confused with acrochier, F.
   accrocher, to hook, get hold of, E. accroach); pref. en- (L.
   in) + F. croc hook. See Crook, and cf. Accroach.]
   To enter by gradual steps or by stealth into the possessions
   or rights of another; to trespass; to intrude; to trench; --
   commonly with on or upon; as, to encroach on a neighbor; to
   encroach on the highway.
   [1913 Webster]

         No sense, faculty, or member must encroach upon or
         interfere with the duty and office of another. --South.
   [1913 Webster]

         Superstition, . . . a creeping and encroaching evil.
                                                  --Hooker.
   [1913 Webster]

         Exclude the encroaching cattle from thy ground.
                                                  --Dryden.

   Syn: To intrude; trench; infringe; invade; trespass.
        [1913 Webster]

WordNet (r) 3.0 (2006):

encroaching
    adj 1: gradually intrusive without right or permission; "we
           moved back from the encroaching tide"; "invasive
           tourists"; "trespassing hunters" [syn: encroaching(a),
           invasive, trespassing(a)]