Vacant area in pub to the rear of lounge (5)
I believe the answer is:
inane
'vacant' is the definition.
(thesaurus)
'area in pub to the rear of lounge' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'in' indicates putting letters inside.
'pub' becomes 'inn' (I've seen this before).
'to the rear of' suggests the final letters.
The last letter of 'lounge' is 'e'.
'a' going into 'inn' is 'inan'.
'inan'+'e'='INANE'
(Other definitions for inane that I've seen before include "Lacking sense, silly" , "Devoid of intelligence" , "Silly, fatuous" , "Frivolous" , "Lacking meaning" .)