quick to notice or perceive; alert.

looking at, watching, or regarding attentively; watchful.

careful in the observing of a law, custom, religious ritual, or the like.

an observer of law or rule.

( initial capital letter ) Also, Observantine

adjective

careless , inattentive , indifferent , thoughtless , unaware , unmindful , unobservant , unwatchful

adjective

advertent , alive , attentive , bright , clear-sighted , comprehending , considering , contemplating , correct , deducing , detecting , discerning , discovering , discriminating , eager , eagle-eyed * , heedful , intelligent , intentive , interested , keen , mindful , not missing a trick , obedient , observative , on one’s toes , on the ball * , penetrating , perceptive , questioning , quick , regardful , searching , sensitive , sharp , sharp-eyed , surveying , understanding , vigilant , wide-awake * , open-eyed , wakeful , wary , watchful , wide-awake , conscious , alert , aware