The Collaborative International Dictionary of English v.0.48:

Unripe \Un*ripe"\, a.
   1. Not ripe; as, unripe fruit.
      [1913 Webster]

   2. Developing too early; premature. --Sir P. Sidney.
      [1913 Webster]

WordNet (r) 3.0 (2006):

unripe
    adj 1: not fully developed or mature; not ripe; "unripe fruit";
           "fried green tomatoes"; "green wood" [syn: green,
           unripe, unripened, immature] [ant: mature,
           ripe]
    2: not fully prepared

Moby Thesaurus II by Grady Ward, 1.0:

166 Moby Thesaurus words for "unripe":
   a bit previous, a novice at, a stranger to, acerb, acerbate,
   acerbic, acescent, adolescent, advanced, at half cock, awkward,
   blankminded, budding, callow, crab, crabbed, dewy, dry, dumb,
   empty, empty-headed, far ahead, fledgling, forward, fresh, gauche,
   green, green as grass, groping, growing, half-baked, half-cocked,
   half-grown, hasty, ignorant, ill-considered, ill-digested,
   ill-seasoned, ill-timed, immature, improper, impubic, impulsive,
   inane, inappropriate, inauspicious, inconvenient, inexpedient,
   inexperienced, infant, infelicitous, ingenuous, innocent,
   inopportune, intact, intempestive, intrusive, irrelevant, juicy,
   juvenile, know-nothing, late, mal a propos, malapropos, minor,
   mistimed, naive, nescient, new to, new-fledged, not firm, off base,
   out of line, out of phase, out of time, overhasty, oversoon,
   pickled, precipitate, precocious, premature, previous, pungent,
   raw, ripening, rushed, sappy, sec, simple, sour, sour as vinegar,
   soured, sourish, strange to, tart, tartish, tender, tentative,
   too early, too late, too soon, unaccustomed to, unacquainted,
   unacquainted with, unadult, unapprized, unbefitting,
   uncomprehending, unconversant, unconversant with, uncrystallized,
   underage, underripe, undeveloped, unenlightened, unexperienced,
   unfamiliar, unfamiliar with, unfavorable, unfit, unfitting,
   unfledged, unformed, unfortunate, ungrown, unhandy, unhappy,
   unilluminated, uninformed, uninitiated, uninitiated in,
   unintelligent, unjelled, unknowing, unlicked, unlucky, unmatured,
   unmeditated, unmellowed, unposted, unpracticed, unpracticed in,
   unpremeditated, unprepared, unpropitious, unready, unseasonable,
   unseasoned, unskilled in, unsuitable, unsure, unsweet, unsweetened,
   untimely, untoward, untried, unused to, unversed, unversed in,
   vacuous, vernal, vinegarish, vinegary, virginal, wrong, youthful