The Collaborative International Dictionary of English v.0.48:

Inopportune \In*op`por*tune"\, a. [L. inopportunus: cf. F.
   inopportun. See In- not, and Opportune.]
   Not opportune; inconvenient; unseasonable; as, an inopportune
   occurrence, remark, etc.
   [1913 Webster]

         No visit could have been more inopportune. --T. Hook.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inopportune
    adj 1: not opportune; "arrived at a most inopportune hour"; "an
           inopportune visit" [ant: opportune]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "inopportune":
   bad, futile, ill-advised, ill-considered, ill-seasoned, ill-suited,
   ill-timed, impolitic, improper, inadvisable, inappropriate, inapt,
   inauspicious, incongruous, inconvenient, inept, inexpedient,
   infelicitous, intempestive, intrusive, irrelevant, late,
   mal a propos, malapropos, mistimed, off base, out of line,
   out of phase, out of place, out of time, premature, too late,
   too soon, unbefitting, undesirable, unfavorable, unfit, unfitting,
   unfortunate, unhandy, unhappy, unlucky, unmeet, unprofitable,
   unpropitious, unready, unripe, unseasonable, unseemly, unsuitable,
   untimely, untoward, unwise, wrong