Peruse underlying facts about primitive duck (9)
I believe the answer is:
goldeneye
'duck' is the definition.
(type of duck)
'peruse underlying facts about primitive' is the wordplay.
'peruse' becomes 'eye' (both can mean to look at).
'underlying' says to put letters next to each other (in a down clue, some letters lie under others).
'facts' becomes 'gen'.
'about' indicates putting letters inside.
'primitive' becomes 'old'.
'gen' placed around 'old' is 'golden'.
'eye' after 'golden' is 'GOLDENEYE'.
(Other definitions for goldeneye that I've seen before include "Northern diving duck - 1995 Bond film" , "spy film" .)