Philosopher a product of Yale, they say (5)
I believe the answer is:
locke
'philosopher' is the definition.
(John Locke)
'a product of yale they say' is the wordplay.
'a product of yale' becomes 'lock' (Yale is a lock manufacturer).
'they say' shows a homophone (sound like).
'lock' is a homophone of 'LOCKE'.
(Other definitions for locke that I've seen before include "English empiricist philosopher, d. 1704" , "A philosopher; sounds like strand of hair" , "John -, seventeenth to eighteenth century English philosopher" .)