Supremo over in British ship (4)
I believe the answer is:
boss
'supremo' is the definition.
Both the definition and answer are singular nouns.
Perhaps you can see an association between them that I can't see?
'over in british ship' is the wordplay.
'over' becomes 'o' (cricket abbreviation).
'in' means one lot of letters goes inside another.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'b'+'ss'='bss'
'o' put into 'bss' is 'BOSS'.
Can you help me to learn more?
(Other definitions for boss that I've seen before include "Manager (colloq.); stud" , "Bully" , "Governor" , "(One's) chief" , "Informal employer or superior" .)