The term 'put on guard' is used to describe the act of warning or cautioning someone. The crossword solutions for this term are WARN (4 letters), WARNED (6 letters), ALARM (5 letters), and CAUTIONED (9 letters). WARN is a verb meaning to give a warning or to notify of danger. WARNED is the past tense of WARN, meaning to have given a warning or to have notified of danger. ALARM is a noun meaning a warning signal or a device that makes a warning sound. CAUTIONED is a verb meaning to WARN or advise someone to be careful.