One may be stranded in gym (4)
I believe the answer is:
rope
'one may' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'stranded in gym' is the wordplay.
'stranded in' becomes 'ro' (I can't explain this - if you can you should give a lot more credence to this answer).
'gym' becomes 'pe' (short for Physical Education).
'ro'+'pe'='ROPE'
'be' acts as a link.
Can you help me to learn more?
(Other definitions for rope that I've seen before include "Cable, cord, hawser" , "Stranded fastener" , "A thick strong cord" , "Tier" , "Pore (anag.)" .)