Queen and socialist strayed (5)
I believe the answer is:
erred
'strayed' is the definition.
('err' can be a synonym of 'stray')
'queen and socialist' is the wordplay.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'and' says to put letters next to each other.
'socialist' becomes 'red' (red is a kind of socialist).
'er'+'red'='ERRED'
(Other definitions for erred that I've seen before include "Sinned" , "Made mistake, was incorrect" , "was inaccurate" , "slipped up" , "Gone astray!" .)