Just me, playing lyre (6)
I believe the answer is:
merely
'just' is the definition.
('merely' can be a synonym of 'just')
'me playing lyre' is the wordplay.
'playing' indicates an anagram.
'lyre' is an anagram of 'rely'.
'me'+'rely'='MERELY'
(Other definitions for merely that I've seen before include "Just one" , "'Only, and nothing more (6)'" , "Simply - only" .)