An event to talk about endlessly (6)
I believe the answer is:
discus
'an event' is the definition.
(athletics event)
'talk about endlessly' is the wordplay.
'talk about' becomes 'discuss' (to discuss something is to talk about it).
'endlessly' means to remove the last letter.
'discuss' with its final letter taken off is 'DISCUS'.
'to' acts as a link.
(Other definitions for discus that I've seen before include "sports event" , "Athletics field event" , "Item thrown in sport" , "Sporting projectile" , "Sporting missile" .)