Alternative piece of a circular path (5)
I believe the answer is:
orbit
'a circular path' is the definition.
(I've seen this in another clue)
'alternative piece' is the wordplay.
'alternative' becomes 'or'.
'piece' becomes 'bit' (synonyms).
'or'+'bit'='ORBIT'
'of' acts as a link.
(Other definitions for orbit that I've seen before include "fly in a circle" , "Sun's circulation" , "Lunar trajectory" , "Track of satellite" , "Circling path" .)