Jettison mouldy cargo? (7)
I believe the answer is:
offload
'jettison' is the definition.
(I've seen this before)
'mouldy cargo?' is the wordplay.
'mouldy' becomes 'off' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'cargo?' becomes 'load' (synonyms).
'off'+'load'='OFFLOAD'
Can you help me to learn more?
(Other definitions for offload that I've seen before include "deliver goods" , "9 [JETTISON]" , "Get rid of (unwanted item or burden)" , "Dump" .)