To make bitter.

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

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.

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