The fortune of a non-U oaf (3)
I believe the answer is:
lot
'the fortune' is the definition.
(as in a person's lot in life)
'a non-u oaf' is the wordplay.
'a non' suggests deleting specific letters.
'oaf' becomes 'lout' (synonyms).
'lout' with 'u' taken away is 'LOT'.
'of' acts as a link.
(Other definitions for lot that I've seen before include "Portion in life" , "He left his wife without a backward glance" , "Great deal; French river" , "Parcel - collection" , "A person's luck" .)