Left tucking into excellent skin of roast pork (9)
I believe the answer is:
crackling
'skin of roast pork' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'left tucking into excellent' is the wordplay.
'left' becomes 'l' (common abbreviation).
'tucking into' means one lot of letters goes inside another.
'excellent' becomes 'cracking' (cracking can mean excellent or brilliant).
'l' going inside 'cracking' is 'CRACKLING'.
Can you help me to learn more?
(Other definitions for crackling that I've seen before include "Crisp skin of pork joint" , "Pork covering" , "Crisp exterior of roast pork" .)