American writer aboard ship beginning to experience anxiety (8)
I believe the answer is:
suspense
'anxiety' is the definition.
(I've seen this before)
'american writer aboard ship beginning to experience' is the wordplay.
'american' becomes 'US' (United States).
'writer' becomes 'pen' (something which writes).
'aboard' indicates putting letters inside.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'beginning to' suggests taking the first letters.
The initial letter of 'experience' is 'e'.
'us'+'pen'='uspen'
'uspen' inserted inside 'ss' is 'suspens'.
'suspens'+'e'='SUSPENSE'
(Other definitions for suspense that I've seen before include "Tense expectation" , "Pre-climactic excitement" , "feature of exciting fiction?" , "Apprehension, anticipation" , "Discontinuance - indecision - excitement" .)