Mention location, say (4)
I believe the answer is:
cite
'mention' is the definition.
(to cite is to mention or quote)
'location say' is the wordplay.
'location' becomes 'site' (site is a kind of location).
'say' indicates a 'sounds like' (homophone) clue.
'site' sounds like 'CITE'.
(Other definitions for cite that I've seen before include "for instance" , "Quote (an author)" , "Quote as authority" , "Quote (eg, a book)" , "Use quotations" .)