Eye that conceals nevertheless (3)
I believe the answer is:
yet
'nevertheless' is the definition.
(thesaurus)
'eye that conceals' is the wordplay.
'conceals' says the answer is hidden in the clue.
'YET' is hidden within 'eye that'.
(Other definitions for yet that I've seen before include "Still; nevertheless" , "Thus far" , "Though; still" , "Up to this time and continuing" , "in spite of that" .)