Write song that shows bias (8)
I believe the answer is:
penchant
'bias' is the definition.
(thesaurus)
'write song' is the wordplay.
'write' becomes 'pen' (synonyms).
'song' becomes 'chant' (song sung by a crowd).
'pen'+'chant'='PENCHANT'
'that shows' is the link.
(Other definitions for penchant that I've seen before include "Inclination; taste" , "Disposition" , "Leaning towards or liking for" , "Fondness (for) - bias (towards)" , "weakness" .)