Airship, second-rate, not rigid (5)
I believe the answer is:
blimp
'airship' is the definition.
(blimp is a kind of airship)
'second-rate not rigid' is the wordplay.
'second rate' becomes 'b'.
'not rigid' becomes 'limp' (I can't explain this - if you can you should believe this answer much more).
'b'+'limp'='BLIMP'
Can you help me to learn more?
(Other definitions for blimp that I've seen before include "needs cover when shooting" , "Airship - barrage balloon" , "David Low's cartoon colonel - airship used for publicity" , "full of hot air?" , "Small nonrigid airship" .)