Ghostly second muscle wanting nothing (8)
I believe the answer is:
spectral
'ghostly' is the definition.
(synonyms)
'second muscle wanting nothing' is the wordplay.
'second' becomes 's' (common abbreviation).
'muscle' becomes 'pectoral' (pectoral is a kind of muscle).
'wanting' is a deletion indicator (to want something can mean to lack it or need it).
'nothing' becomes 'o' (looks like zero - 0).
'pectoral' with 'o' taken out is 'pectral'.
's'+'pectral'='SPECTRAL'
(Other definitions for spectral that I've seen before include "Ghastly" , "Rap Celts for being ghostly" , "Ghostly; of bands of colour" , "Like a colourful band" , "Spooky" .)