Sailor held by Communist worker, causing delay (9)
I believe the answer is:
retardant
'delay' is the definition.
Both the answer and definition are singular nouns.
Perhaps you can see an association between them that I don't see?
'sailor held by communist worker' is the wordplay.
'sailor' becomes 'tar' (tar can mean a sailor).
'held by' indicates putting letters inside.
'communist' becomes 'red' (red can informally mean communist).
'worker' becomes 'ant' (worker is a type of ant).
'tar' going within 'red' is 'retard'.
'retard'+'ant'='RETARDANT'
'causing' is the link.
Can you help me to learn more?
(Other definitions for retardant that I've seen before include "It delays" , "Inhibiting substance" , "Preventing, inhibiting" , "having slowing effect" , "Substance suppressing fire" .)