observant — ODE

observant /əbˈzəːvnt

▸ adjective

1 quick to notice or perceive things:

her observant eye took in every detail.

2 adhering strictly to the rules of a particular religion, especially Judaism:

an observant Jew.

▸ noun historical (Observant) a member of a branch of the Franciscan order that followed a strict rule.

– ORIGIN late Middle English (as a noun): from French, literally ‘watching’, present participle of observer (see observe).