1) quick at noticing things (observant)
2) the act, state, of observing or being observed; the power of noticing carefully (observation)
3) not quick at noticing things (unobservant)
able to think, feel, see etc.
alert, awake
to use one's ability to see in order to search, examine, be entertained etc
visual examination
(especially) a pattern of colours of feathers, fur etc
designating
the act, state, of observing or being observed; the power of noticing carefully
attention, scrutiny
the act of recognizing or being recognized
identification, acknowledgment