Bring chopper down here, smashing part of mouth into skull (7)
I believe the answer is:
helipad
'bring chopper down here smashing part' is the definition.
The definition suggests a singular noun which matches the answer.
'mouth into skull' is the wordplay.
'mouth' becomes 'lip' (synonyms).
'into' means one lot of letters goes inside another.
'skull' becomes 'head' (I've seen this before).
'lip' put into 'head' is 'HELIPAD'.
'of' is the link.
Can you help me to learn more?
(Other definitions for helipad that I've seen before include "Chopper comes down here" , "Where chopper lands" , "anding area" , "Vertical take-off and landing area" , "Landing area for copters" .)