They may cover optics (4)
I believe the answer is:
lids
'they' is the definition.
Both the answer and definition are plural nouns.
Maybe there's an association between them I don't understand?
'cover optics' is the wordplay.
'cover' becomes 'lid' (lid is a kind of cover).
'optics' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'lid'+'s'='LIDS'
'may' is the link.
Can you help me to learn more?
(Other definitions for lids that I've seen before include "Eye covers" , "Movable tops or covers" , "Covers for opening and closing" .)