The Collaborative International Dictionary of English v.0.48:

malapropos \mal*ap"ro*pos`\, a. & adv. [F. mal [`a] propos; mal
   evil + [`a] propos to the purpose.]
   Unseasonable or unseasonably; unsuitable or unsuitably.
   [1913 Webster]

WordNet (r) 3.0 (2006):

malapropos
    adv 1: at an inconvenient time; "he arrived inopportunely just
           as we sat down for dinner"; "she answered malapropos"
           [syn: inopportunely, malapropos] [ant: opportunely]
    adj 1: of an inappropriate or incorrectly applied nature [ant:
           apropos]

Moby Thesaurus II by Grady Ward, 1.0:

81 Moby Thesaurus words for "malapropos":
   bad, futile, ill-adapted, ill-advised, ill-assorted, ill-chosen,
   ill-considered, ill-fitted, ill-matched, ill-seasoned, ill-sorted,
   ill-suited, ill-timed, impolitic, improper, inadmissible,
   inadvisable, inapplicable, inapposite, inappropriate, inapt,
   inauspicious, incongruous, inconvenient, inept, inexpedient,
   infelicitous, inopportune, intempestive, intrusive, irrelevant,
   late, mal a propos, maladjusted, misjoined, mismatched, mismated,
   misplaced, mistimed, off base, out of character, out of joint,
   out of keeping, out of line, out of phase, out of place,
   out of proportion, out of season, out of time, out of tune,
   premature, too late, too soon, unadapted, unapt, unbecoming,
   unbefitting, undesirable, undue, unfavorable, unfit, unfitted,
   unfitting, unfortunate, unhandy, unhappy, unlucky, unmeet,
   unprofitable, unpropitious, unqualified, unready, unripe,
   unseasonable, unseemly, unsuitable, unsuited, untimely, untoward,
   unwise, wrong