Pendulum clock component that's exactly round (8)
I believe the answer is:
deadbeat
'pendulum clock component' is the definition.
I can't judge whether this defines the answer.
'exactly round' is the wordplay.
'exactly' becomes 'dead' (eg in phrases like 'you're dead right').
'round' becomes 'beat' (synonyms).
'dead'+'beat'='DEADBEAT'
'that's' is the link.
Can you help me to learn more?
(Other definitions for deadbeat that I've seen before include "down-and-out" , "Lazy, useless person" , "lazy so-and-so" , "lazy fellow" , "Disreputable person" .)