Excellent railway regalia (6)
I believe the answer is:
finery
'regalia' is the definition.
(synonyms)
'excellent railway' is the wordplay.
'excellent' becomes 'fine' (synonyms).
'railway' becomes 'ry' (abbreviation for railway).
'fine'+'ry'='FINERY'
(Other definitions for finery that I've seen before include "Elaborate clothes and accessories" , "Ostentatious decoration" , "Showy clothing" , "Elaborate clothing, jewellery etc" , "Ostentatious clothing" .)