Part of the eye containing a clear piece, one finds (6)
I believe the answer is:
learns
'one finds' is the definition.
The definition and answer can be both related to thinking as well as being verbs in their -s form.
Perhaps you can see a link between them that I don't see?
'part of the eye containing a clear piece' is the wordplay.
'part of the eye' becomes 'lens' ('lens' is part of 'eye').
'containing' is an insertion indicator.
'clear piece' becomes 'r' (abbreviation for Rook. I am not sure about the 'clear' bit.).
'a'+'r'='ar'
'lens' placed around 'ar' is 'LEARNS'.
Can you help me to learn more?
(Other definitions for learns that I've seen before include "Teaches non-standard" , "Imbibes knowledge" , "Gains knowledge or skills" , "Finds out" , "Acquires knowledge as in class" .)