Plain holiday home providing accommodation for one (7)
I believe the answer is:
vanilla
'plain' is the definition.
(I've seen this before)
'holiday home providing accommodation for one' is the wordplay.
'holiday home' becomes 'villa ' (I've seen this before).
'providing accommodation for' is an insertion indicator.
'one' becomes 'an' (an apple is one apple).
'villa' placed around 'an' is 'VANILLA'.
(Other definitions for vanilla that I've seen before include "Pod that produces flavouring" , "Pods to flavour, ice-cream, say" , "Common ice cream flavour" , "lacking any special features" , "Flavouring from orchid pods" .)