Return of American poet mostly creates excitement (8)
I believe the answer is:
suspense
'excitement' is the definition.
(synonyms)
'return of american poet mostly' is the wordplay.
'return' says the letters should be written in reverse.
'of american' becomes 'US' (United States).
'poet' becomes 'Spenser' (16th-century poet Edmund Spenser).
'mostly' means to remove the last letter (most but not all of the word).
'us' written backwards gives 'su'.
'spenser' with its last letter taken away is 'spense'.
'su'+'spense'='SUSPENSE'
'creates' acts as a link.
(Other definitions for suspense that I've seen before include "Uncertain state" , "The 3 of having to wait" , "Uncertain anticipation" , "State of anxiety or excitement" , "State of uncertainty or excitement" .)