Float with a marine crew (7)
I believe the answer is:
armband
'float' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'with a marine crew' is the wordplay.
'with' means one lot of letters go next to another.
'marine' becomes 'RM' (abbreviation for Royal Marine).
'crew' becomes 'band' (both can mean a group of people).
'a' put next to 'rm' is 'arm'.
'arm'+'band'='ARMBAND'
Can you help me to learn more?
(Other definitions for armband that I've seen before include "Identification worn on sleeve" , "Cloth worn round sleeve" , "Inflatable aid for those learning to swim" , "Loop for holding up a shirtsleeve" , "What might hold up sleeve" .)