The Oxford Thesaurus An A-Z Dictionary of Synonyms - observant adj.

1) watchful, alert, attentive, vigilant, on the lookout, on the qui vive, on guard, wide awake, regardful, mindful, aware, keen, keen-eyed, sharp-eyed, eagle-eyed, perceptive, sharp, shrewd: Hannay was observant of all who passed him on the way to the train. How very observant of you to spot the man in the crowd! 2 Usually, observant of. obedient (to) , compliant (with) , respectful (of) , heedful(of) , attentive (to or of) , conformist (to) , adherent (to) : One must be always be observant of the rules of the road.