Observers usually working in pairs (4)
I believe the answer is:
eyes
This clue could be a double definition.
'observers' is the first definition.
Although both the answer and definition are plural nouns, I don't see how one could define the other.
'usually working in pairs' is the second definition.
Although both the answer and definition are verbs in their -s form, I don't see how one could define the other.
Can you help me to learn more?
(Other definitions for eyes that I've seen before include "Peacock's tail markings" , "They see and" , "Witnesses" , "Openings" , "Peepers" .)