It propels rocket heading off (3)
I believe the answer is:
oar
'it propels' is the definition.
The definition suggests a singular noun which matches the answer.
'rocket heading off' is the wordplay.
'rocket' becomes 'soar' (I've seen this in another clue).
'heading off' means to remove the first letter.
'soar' with its initial letter taken off is 'OAR'.
Can you help me to learn more?
(Other definitions for oar that I've seen before include "Rowing device" , "Rower" , "Implement to propel a boat" , "Rowing boat operator" , "Rower's paddle" .)