I. adjective
1.
Synonyms: watchful , open-eyed, unsleeping, vigilant, wakeful, wide-awake
Related Word: attentive, heedful, mindful; careful
Idioms: all eyes and ears, on (one's) guard, on the alert
Contrasted words: inattentive, unmindful; aloof, detached, indifferent, unconcerned
2.
Synonyms: intelligent 2, brainy, bright, brilliant, clever, knowing, quick-witted, ready-witted, sharp, smart
Related Word: apt, prompt, quick, ready
Contrasted words: lackadaisical, languid, listless
3.
Synonyms: lively 1, animated, ||cant, ||canty, gay, keen, spirited, sprightly, unpedantic, vivacious
Related Word: frisky; mercurial
Idioms: full of life
Contrasted words: inactive, indolent
Antonyms: inert
II. noun
Synonyms: alarm 1, SOS, tocsin