Spice Girl's a little sad about track (5)
I believe the answer is:
scary
'spice girl's' is the definition.
(nickname of Melanie Brown in the Spice Girls)
'a little sad about track' is the wordplay.
'a little' suggests taking the first letters.
'about' becomes 'ca' (short for circa).
'track' becomes 'RY' (abbreviation for railway).
The first letter of 'sad' is 's'.
's'+'ca'+'ry'='SCARY'
(Other definitions for scary that I've seen before include "Alarming, maybe paranormal" , "Hair-raising" , "[SPICE]" , "spook" , "Fearsome" .)