'Shut up!', said the philosopher (5)
I believe the answer is:
locke
'philosopher' is the definition.
(John Locke)
'shut up said' is the wordplay.
'shut up' becomes 'lock' (synonyms).
'said' indicates a 'sounds like' (homophone) clue.
'lock' sounds like 'LOCKE'.
'the' acts as a link.
(Other definitions for locke that I've seen before include "John -, seventeenth to eighteenth century English philosopher" , "English empiricist philosopher, d. 1704" , "A philosopher; sounds like strand of hair" .)