Golf - I lost (4)
I believe the answer is:
gone
'lost' is the definition.
('gone' can be a synonym of 'lost')
'golf i' is the wordplay.
'golf' becomes 'g' (phonetic alphabet: alpha, bravo, charlie etc.).
'i' becomes 'one' ('one' can be a synonym of 'i'**).
'g'+'one'='GONE'
(Other definitions for gone that I've seen before include "Departed or no longer available" , "Departed or dead" , "Departed, disappeared" , "Away, departed" , "No longer present" .)