The Collaborative International Dictionary of English v.0.48:

Undesigned \Undesigned\
   See designed.

WordNet (r) 3.0 (2006):

undesigned
    adj 1: not done or made or performed with purpose or intent
           [ant: designed, intentional]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "undesigned":
   automatic, casual, gut, ill-advised, ill-considered, ill-devised,
   inadvertent, indeliberate, involuntary, reflex, reflexive, snap,
   spontaneous, unadvised, uncalculated, unconscious, unconsidered,
   undeliberate, undeliberated, undevised, unguarded, unguided,
   unintended, unintentional, unmeant, unmeditated, unplanned,
   unpremeditated, unprompted, unpurposed, unstudied, unthinking,
   unthought, unthought-of, unwilled, unwitting