American Dictionary of the English Language

IMBIT'TER, verb transitive [in and bitter.] To make bitter.

1. To make unhappy or grievous; to render distressing. The sins of youth often imbitter old age. Grief imbitters our enjoyments.

2. To exasperate; to make more severe, poignant or painful. The sorrows of true penitence are imbittered by a sense of our ingratitude to our Almighty Benefactor.

3. To exasperate; to render more violent or malignant; as, to imbitter enmity, anger, rage, passion, etc.