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