Bitterness of a professional lacking in good fortune (8)
I believe the answer is:
asperity
'bitterness of a professional lacking in good fortune' is the definition.
'asperity' can be an answer for 'bitterness' (asperity is bitterness or sharpness in one's tone). I am unsure of the 'of a professional lacking in good fortune' bit.
'bitterness of a professional lacking in good fortune' is the wordplay.
'bitterness of' becomes 'a' (I can't justify this - if you can you should give a lot more credence to this answer).
'a professional' becomes 'pro' ('pro' can be a synonym of 'professional').
'lacking in' is a deletion indicator.
'good fortune' becomes 'prosperity' (prosperity is a kind of good fortune).
'prosperity' with 'pro' taken out is 'sperity'.
'a'+'sperity'='ASPERITY'
(Other definitions for asperity that I've seen before include "Harshness of tone or manner" , "Harshness, bitter coldness" , "Harshness or severity of manner" , "rough manner" , "'Sharpness, harshness (8)'" .)