adjective
Synonyms: watchful , alert, open-eyed, unsleeping, wakeful, wide-awake
Related Word: agog, anxious, avid, eager, keen; acute, sharp, sharp-eyed; attentive
Idioms: on one's guard, with a weather eye open
Contrasted words: lax, neglectful, negligent, remiss, slack; forgetful, oblivious, unmindful