Cheerful greeting announced (4)
I believe the answer is:
high
'cheerful' is the definition.
(I've seen this before)
'greeting announced' is the wordplay.
'greeting' becomes 'hi' (hi is a kind of greeting).
'announced' shows a homophone (sound like).
'hi' sounds like 'HIGH'.
(Other definitions for high that I've seen before include "Drunk; anticyclone" , "Elevated; euphoric" , "up a mountain?" , "Cheerful" , "Important, elevated" .)