Airship beginning to become soft (5)
I believe the answer is:
blimp
'airship' is the definition.
(blimp is a kind of airship)
'beginning to become soft' is the wordplay.
'beginning to' suggests taking the first letters.
'soft' becomes 'limp' (I can't explain this - if you can you should give a lot more credence to this answer).
The first letter of 'become' is 'b'.
'b'+'limp'='BLIMP'
Can you help me to learn more?
(Other definitions for blimp that I've seen before include "full of hot air?" , "Barrage balloon; backwoods Colonel" , "returns one pound to provost" , "Elderly pompous reactionary person" , "Small barrage balloon" .)