Japan referee lives in new hotel (7)
I believe the answer is:
varnish
'japan' is the definition.
(I've seen this before)
'referee lives in new hotel' is the wordplay.
'referee' becomes 'VAR' (video assistant referee).
'lives' becomes 'is' ('be' can be a synonym of 'live').
'in' indicates putting letters inside.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'n'+'h'='nh'
'is' going into 'nh' is 'nish'.
'var'+'nish'='VARNISH'
(Other definitions for varnish that I've seen before include "It is applied to wood to make it shine" , "Lacquer" , "Coating for wood, etc" , "Hard, glossy, transparent coating" , "Glossy coat" .)