The Collaborative International Dictionary of English v.0.48:

Unfamiliar \Unfamiliar\
   See familiar.

WordNet (r) 3.0 (2006):

unfamiliar
    adj 1: not known or well known; "a name unfamiliar to most"; "be
           alert at night especially in unfamiliar surroundings"
           [ant: familiar]

Moby Thesaurus II by Grady Ward, 1.0:

109 Moby Thesaurus words for "unfamiliar":
   able, awkward, bizarre, blankminded, breakaway, callow, curious,
   different, dumb, empty, empty-headed, enigmatic, exotic, foreign,
   gauche, green, groping, ignorant, inane, incalculable,
   incognizable, incognizant, inexperienced, innocent, know-nothing,
   mysterious, naive, nescient, new, novel, oblivious, odd, offbeat,
   original, peculiar, puzzling, rare, raw, recherche, remarkable,
   sealed, simple, strange, strange to, sui generis, tentative,
   unaccustomed, unaccustomed to, unacquainted, unacquainted with,
   unapparent, unapprehended, unapprized, unascertained, unaware,
   unbeknown, uncharted, unclassified, uncommon, uncomprehending,
   unconventional, unconversant, unconversant with, uncustomary,
   undisclosed, undiscoverable, undiscovered, undivulged,
   undreamed-of, unenlightened, unexpected, unexplained, unexplored,
   unexposed, unfamiliar with, unfathomed, unheard, unheard-of,
   unidentified, unilluminated, uninformed, uninitiated,
   uninitiated in, uninstructed, unintelligent, uninvestigated,
   unique, unknowable, unknowing, unknown, unordinary, unperceived,
   unplumbed, unposted, unrevealed, unripe, unskilled in, unsure,
   unsuspected, unthought-of, untouched, unused to, unusual, unversed,
   unversed in, unwitting, unwonted, vacuous, virgin