Soldier with swimmer and aviator on the periphery (6)
I believe the answer is:
hussar
'soldier' is the definition.
(I know that hussar is a type of cavalryman)
'swimmer and aviator on the periphery' is the wordplay.
'swimmer' becomes 'huss' (huss is a type of fish).
'and' means one lot of letters go next to another.
'on the periphery' means to remove the middle letters (only letters on the periphery of the word).
'aviator' with its centre removed is 'ar'.
'huss'+'ar'='HUSSAR'
'with' acts as a link.
(Other definitions for hussar that I've seen before include "Cavalryman, originally Hungarian" , "Member of a light cavalry regiment" , "Horseman" , "Soldier in a light cavalry regiment" , "one often up on a charge" .)