Philosopher in bar, did you say? (5)
I believe the answer is:
locke
'philosopher' is the definition.
(John Locke)
'bar did you say?' is the wordplay.
'bar' becomes 'lock' (I've seen this in other clues).
'did you say?' shows a homophone (sound like).
'lock' sounds like 'LOCKE'.
'in' acts as a link.
(Other definitions for locke that I've seen before include "A philosopher; sounds like strand of hair" , "John -, seventeenth to eighteenth century English philosopher" , "English empiricist philosopher, d. 1704" .)