Cheerful readiness (8)
I believe the answer is:
alacrity
'cheerful readiness' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for alacrity that I've seen before include "Enthusiastic speed" , "'Quick, cheerful enthusiasm (8)'" , "Prompt enthusiasm" , "Prompt readiness and briskness" , "Prompt and eager readiness" .)