Friend has one bucket (4)
I believe the answer is:
pail
'bucket' is the definition.
(synonyms)
'friend has one' is the wordplay.
'friend' becomes 'pal' (pal can mean a friend).
'has' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'pal' going around 'i' is 'PAIL'.
(Other definitions for pail that I've seen before include "A bucket - the kind Jack and Jill used" , "Vessel for carrying liquids" , "Cylindrical vessel" , "water-carrier" , "it may go down well" .)