The Collaborative International Dictionary of English v.0.48:

Polytechnic \Pol`y*tech"nic\ (p[o^]l`[i^]*t[e^]k"n[i^]k), a.
   [Gr. poly`technos; poly`s many + te`chnh an art: cf. F.
   polytechnique.]
   Comprehending, or relating to, many arts and sciences; --
   applied particularly to schools in which many branches of art
   and science are taught with especial reference to their
   practical application; as, a polytechnic institute; also to
   exhibitions of machinery and industrial products.
   [1913 Webster]

WordNet (r) 3.0 (2006):

polytechnic
    n 1: a technical school offering instruction in many industrial
         arts and applied sciences [syn: polytechnic institute,
         polytechnic, engineering school]