Exhaust me, returning to America retired (8)
I believe the answer is:
emeritus
'retired' is the definition.
(synonyms)
'exhaust me returning to america' is the wordplay.
'exhaust' becomes 'tire' (synonyms).
'returning' says the letters should be written backwards.
'to america' becomes 'US' (United States).
'tire'+'me'='tireme'
'tireme' back-to-front is 'emerit'.
'emerit'+'us'='EMERITUS'
(Other definitions for emeritus that I've seen before include "Professor retired from regular work" , "Use remit for retained title of retired professional" , "Retired, but retaining the title of one's office" , "Title given to retired professor" , "Honourably retired but retaining title" .)