A cornet, or parts of one (4)
I believe the answer is:
cone
'a cornet' is the definition.
(thesaurus)
'parts of one' is the wordplay.
'parts of' becomes 'c' (I can't justify this - if you can you should give a lot more credence to this answer).
'c'+'one'='CONE'
'or' acts as a link.
Can you help me to learn more?
(Other definitions for cone that I've seen before include "may obstruct lane" , "Tapering object" , "99, maybe" , "Element of geometry" , "Geometrical figure (used on roads!)" .)