observant

adjective

1 lifeguards should be observant and stop risky situations before they start:

alert, sharp-eyed, sharp, eagle-eyed, hawk-eyed, with eyes like a hawk, keen-eyed, watchful, on the lookout, on the qui vive, on guard, attentive, vigilant, hypervigilant, with one's eyes open/peeled/skinned, awake, heedful, mindful, focused, aware;

informal beady-eyed, not missing a trick, on the ball;

rare regardful.

▷antonyms inattentive, dreamy.

2 an observant Jew:

practising, obedient, dutiful, conformist, conforming;

committed, devout, orthodox, law-abiding.

observant Oxford Dictionary of English