Courteous worker faced with bitterness (7)
I believe the answer is:
gallant
'courteous' is the definition.
(similar in meaning)
'worker faced with bitterness' is the wordplay.
'worker' becomes 'ant' (worker is a type of ant).
'faced with' says to put letters next to each other (some letters act as the front or face of the word).
'bitterness' becomes 'gall' (synonyms).
'ant' put after 'gall' is 'GALLANT'.
(Other definitions for gallant that I've seen before include "markedly attentive to women" , "lady-killer?" , "Daring" , "Brave and chivalrous like knight of old" , "Bold" .)