Service in French is for an artist (5)
I believe the answer is:
ernst
'an artist' is the definition.
(max ernst)
'service in french is' is the wordplay.
'service' becomes 'rn' (abbreviation for Royal Navy).
'in' is an insertion indicator.
'french is' becomes 'est' ('is' in the French language).
'rn' going inside 'est' is 'ERNST'.
'for' acts as a link.
(Other definitions for ernst that I've seen before include "Surrealist; stern (anag.)" , "Max --, German painter" , "German-born painter, Max, co-founder of dadaism, d. 1976" , "Max -, twentieth century German Surrealist artist" , "Young partner" .)