Circling or piercing? (8)
I believe the answer is:
orbiting
'circling' is the definition.
(orbiting is a kind of circling)
'or piercing?' is the wordplay.
'piercing?' becomes 'biting' (biting is a kind of piercing).
'or'+'biting'='ORBITING'
(Other definitions for orbiting that I've seen before include "Going around in circles - is It boring?" , "Moving around a body in space" , "Going round in circles" , "In a kind of revolution" , "Travelling around" .)