Pest is occupying shade (8)
I believe the answer is:
nuisance
'pest' is the definition.
(thesaurus)
'is occupying shade' is the wordplay.
'occupying' means one lot of letters goes inside another.
'shade' becomes 'nuance' ('nuance' can be a synonym of 'shade'**).
'is' placed inside 'nuance' is 'NUISANCE'.
(Other definitions for nuisance that I've seen before include "Something which annoys" , "It causes inconvenience or annoyance" , "troublesome type" , "Annoying thing/person" , "Bothersome annoying person" .)