Synonyms and related words :
automatic, casual, gut, ill-advised, ill-considered, ill-devised, inadvertent, indeliberate, involuntary, reflex, reflexive, snap, spontaneous, unadvised, unconscious, unconsidered, undeliberate, undeliberated, undesigned, unintended, unintentional, unmeditated, unpremeditated, unstudied, unwilled