Bitterness in a continental soldier is caddish (9)
I believe the answer is:
ungallant
'caddish' is the definition.
('ungallant' can be a synonym of 'caddish')
'bitterness in a continental soldier' is the wordplay.
'bitterness' becomes 'gall' ('gall' can be a synonym of 'bitterness').
'in' indicates putting letters inside.
'a continental' becomes 'un' (the word 'a' as said on the European continent).
'soldier' becomes 'ant' (I've seen this before).
'un'+'ant'='unant'
'gall' going inside 'unant' is 'UNGALLANT'.
'is' is the link.
(Other definitions for ungallant that I've seen before include "lacking courtesy" , "ignoble" , "Not chivalrous" , "Discourteous" .)