The Collaborative International Dictionary
Imbitter \Im*bit"ter\, v. t. [imp. & p. p. Imbittered; p. pr. & vb. n. Imbittering.] [Pref. im- in + bitter. Cf. Embitter.] [Written also embitter.] To make bitter; hence, to make distressing or more distressing; to make sad, morose, sour, or malignant.
Is there anything that more imbitters the enjoyment of
this life than shame?
--South.
Imbittered against each other by former contests.
--Bancroft.
Wiktionary
vb. (en-past of: imbitter)
Usage examples of "imbittered".
He had fought upon the King's side in all the late wars, and had at Shrewsbury received a wound that unfitted him for active service, so that now he was fallen to the post of Captain of Esquires at Devlen Castle--a man disappointed in life, and with a temper imbittered by that failure as well as by cankering pain.
The resentment of the people was imbittered by some previous disputes.
Capricious pardon and arbitrary punishment imbittered the irksomeness and discontent of a long reign: a conspiracy was formed in the palace.