Besotted girl bewailed losing knight (9)
I believe the answer is:
enamoured
'besotted' is the definition.
(I've seen this before)
'girl bewailed losing knight' is the wordplay.
'girl' becomes 'ena' (I've seen this in other clues).
'bewailed' becomes 'mourned' (wail can mean to mourn).
'losing' suggests deleting specific letters.
'knight' becomes 'N' (chess abbreviation).
'mourned' with 'n' removed is 'moured'.
'ena'+'moured'='ENAMOURED'
(Other definitions for enamoured that I've seen before include "In love with - named rou (anag)" , "Besotted" , "Inspired with love" , "Our mean Ed (anag.)" , "Charmed" .)