Cover is void except on vacation (7)
I believe the answer is:
blanket
'cover' is the definition.
(blanketing is a kind of covering)
'void except on vacation' is the wordplay.
'void' becomes 'blank' (I've seen this before**).
'on vacation' suggests removing the centre.
'except' with its centre taken out is 'et'.
'blank'+'et'='BLANKET'
'is' acts as a link.
(Other definitions for blanket that I've seen before include "Woollen bed cover" , "Covering all cases" , "Thick item on bed" , "coating" , "Comprehensive" .)