Frogmen (6)
I believe the answer is:
divers
'frogmen' is the definition.
('diver' can be a synonym of 'frogman')
This is all the clue.
(Other definitions for divers that I've seen before include "Several; snorkellers" , "Penguins, say" , "footballers cheating" , "Some water-birds; assorted" , "Plungers" .)