The Collaborative International Dictionary of English v.0.48:

Frictionless \Fric"tion*less\, a.
   Having no friction.
   [1913 Webster]

WordNet (r) 3.0 (2006):

frictionless
    adj 1: lacking all friction; "a perpetual motion machine would
           have to be frictionless"

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "frictionless":
   accordant, agreeable, agreeing, akin, amicable, at one, attuned,
   compatible, concordant, congenial, corresponding, easy-flowing,
   easy-running, empathetic, empathic, en rapport, harmonious,
   in accord, in concert, in rapport, in tune, inharmony, like-minded,
   of one mind, peaceful, smooth-running, sympathetic, together,
   understanding, united, well-oiled