Unremarkable article in large residence (7)
I believe the answer is:
vanilla
'large residence' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'unremarkable article in' is the wordplay.
'unremarkable' becomes 'villa' (I am not sure about this - if you are sure you should believe this answer much more).
'article' becomes 'an' (indefinite article).
'in' means one lot of letters goes inside another.
'villa' enclosing 'an' is 'VANILLA'.
Can you help me to learn more?
(Other definitions for vanilla that I've seen before include "conventional" , "Nice flavouring for ice-cream" , "Plain" , "Popular ice-cream, flavour" , "plant" .)