One from the Panto has large country house that's very trendy (7)
I believe the answer is:
villain
'one from the panto' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'large country house that's very trendy' is the wordplay.
'large country house' becomes 'villa' (I've seen this before).
'that's' means one lot of letters go next to another.
'very trendy' becomes 'in' (I am not sure about the 'very' bit.**).
'villa'+'in'='VILLAIN'
'has' is the link.
Can you help me to learn more?
(Other definitions for villain that I've seen before include "One played badly" , "Principal wicked character" , "Evil character" , "Principal fictional baddie" , "Criminal; stage baddy" .)