WordNet (r) 3.0 (2006):

unacquainted with
    adj 1: having little or no knowledge of; "unacquainted with city
           ways" [syn: unacquainted(p), unacquainted with(p),
           unfamiliar with(p)]

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "unacquainted with":
   a novice at, a stranger to, awkward, blankminded, callow,
   disaccustomed, dumb, empty, empty-headed, fresh, gauche, green,
   green as grass, groping, ignorant, immature, inane, inexperienced,
   innocent, know-nothing, naive, nescient, new to, raw, rusty,
   simple, strange to, tentative, unaccustomed, unaccustomed to,
   unacquainted, unapprized, uncomprehending, unconversant,
   unconversant with, undeveloped, unenlightened, unexperienced,
   unfamiliar, unfamiliar with, unfledged, unhabituated, unhardened,
   unilluminated, uninformed, uninitiated, uninitiated in,
   unintelligent, uninured, unknowing, unmatured, unposted,
   unpracticed, unpracticed in, unripe, unseasoned, unskilled in,
   unsure, untrained, untried, unused, unused to, unversed,
   unversed in, unwonted, vacuous, weaned