Synonyms for Imprudent (same or very similar meaning)
WordNet sense 1 (imprudently incurring risk):
rashWordNet sense 2 (lacking or showing lack of judgment or discretion; unwise):
injudiciousWordNet sense 3 (not given careful consideration):
improvidentWordNet sense 4 (lacking discretion; injudicious):
indiscreetFrom the ODE community, based on WordNetadd/edit