American, as it happens, is quick (5)
I believe the answer is:
alive
'quick' is the definition.
(I've seen this before)
'american as it happens' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'as it happens' becomes 'live' (as in live broadcasting).
'a'+'live'='ALIVE'
'is' is the link.
(Other definitions for alive that I've seen before include "Functioning" , "answer, as it happens" , "Alert, active" , "full of vitality" , "Animated, on the ball" .)