American quiet in feeling doubt (8)
I believe the answer is:
suspense
'doubt' is the definition.
(suspense is a kind of doubt)
'american quiet in feeling' is the wordplay.
'american' becomes 'us'.
'quiet' becomes 'p' (music symbol for 'piano').
'in' means one lot of letters goes inside another.
'feeling' becomes 'sense' (I've seen this before).
'us'+'p'='usp'
'usp' put into 'sense' is 'SUSPENSE'.
(Other definitions for suspense that I've seen before include "Tense expectation" , "Feeling of excitement or anxiety about what might happen" , "The 3 of having to wait" , "Nervous uncertainty; cessation" , "State of apprehension about what's going to happen" .)