The term 'on guard' is used to describe a state of being PREPARED and ALERT for potential danger. The crossword solutions LEERY (5 letters), PREPARED (8 letters), READY (5 letters), HEEDFUL (7 letters), ATTENTIVE (9 letters), WARY (4 letters), ALERT (5 letters), CHARY (5 letters), VIGILANT (8 letters), WATCHFUL (8 letters), OBSERVANT (9 letters), and PROTECTIVE (10 letters) all describe this state of readiness. Being LEERY means to be cautious and suspicious, while being PREPARED means to be READY for any situation. Being READY implies that one is PREPARED for action, while being HEEDFUL means to pay attention to warnings. Being ATTENTIVE means to be aware of one's surroundings, while being WARY means to be on the lookout for potential danger. Being ALERT means to be READY to respond to any situation, while being CHARY means to be careful and cautious. Being VIGILANT means to be constantly WATCHFUL, while being WATCHFUL means to be ALERT and ATTENTIVE. Being OBSERVANT means to be aware of one's environment, and being PROTECTIVE means to take measures to ensure safety.