Disturbed rest with clap that's ghostly (8)
I believe the answer is:
spectral
'that's ghostly' is the definition.
(synonyms)
'disturbed rest with clap' is the wordplay.
'disturbed' indicates anagramming the letters (the order of letters is disturbed).
'with' means one lot of letters go next to another.
'rest' put after 'clap' is 'claprest'.
'claprest' anagrammed gives 'SPECTRAL'.
(Other definitions for spectral that I've seen before include "Rap Celts for being ghostly" , "Of or like a ghost" , "Like a colourful band" , "Ghastly" , "Spooky" .)