Romantic concept is accepted by officer (8)
I believe the answer is:
idealist
'romantic' is the definition.
(thesaurus)
'concept is accepted by officer' is the wordplay.
'concept' becomes 'idea' (I've seen this before**).
'accepted by' means one lot of letters goes inside another.
'officer' becomes 'lt' (I've seen this in other clues).
'is' inserted into 'lt' is 'list'.
'idea'+'list'='IDEALIST'
(Other definitions for idealist that I've seen before include "Sail tide (anag.)" , "One seeking perfection" , "man of principle" , "Person who acts from the highest motivations" , "One who aims for perfection, may be unrealistic" .)