unprepared adjective 1noun 1forms 3 adjective1 •Not prepared; caught by surprise.The castle was unprepared for the assault. noun1 •A black mark given to a pupil who arrives at a lesson without the necessary items or preparation."He's got another rule: Whenever he gets three unprepareds in a row, he leaves the classroom." — 1983 formsunprepareds · more unprepared · most unprepared