Working during early spring for sovereign (7)
I believe the answer is:
monarch
'sovereign' is the definition.
(synonyms)
'working during early spring' is the wordplay.
'working' becomes 'on' (on can mean working or activated).
'during' means one lot of letters goes inside another.
'early spring' becomes 'March' (first month of spring).
'on' going inside 'march' is 'MONARCH'.
'for' acts as a link.
(Other definitions for monarch that I've seen before include "Not a subject" , "Butterfly - ruler" , "Butterfly (emperor, say?)" , "Crowned head" , "Stag in Landseer picture" .)