Spare part boom? (4)
I believe the answer is:
spar
This clue could be a double definition.
'spare part' is the first definition.
'spar' can be an answer for 'part' (I have seen 'Part of rigging' mean 'spar' so perhaps 'part' could also mean 'spar'). I am not sure about the 'spare' bit.
'boom?' is the second definition.
(boom is a kind of spar)
Can you help me to learn more?
(Other definitions for spar that I've seen before include "dispute" , "Box for practice" , "Fight - something probably rigged?" , "Pole to support sails, rigging etc" , "Box (lightly) - fight (verbally)" .)