Sign nothing's missing in substandard holiday accommodation (7)
I believe the answer is:
portent
'sign' is the definition.
(a portent is a sign of something)
'nothing's missing in substandard holiday accommodation' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'missing in' is a deletion indicator.
'substandard' becomes 'poor' (I've seen this in another clue).
'holiday accommodation' becomes 'tent' (I can't justify this - if you can you should believe this answer much more).
'poor' with 'o' taken out is 'por'.
'por'+'tent'='PORTENT'
Can you help me to learn more?
(Other definitions for portent that I've seen before include "Sign or warning of an event likely to happen" , "bad sign" , "Sign of thing to come" , "Warning of momentous event" , "Foreboding" .)