Webster’s Revised Unabridged Dictionary · 1913
Imbitter
Im·bit′ter (ĭm·bĭt′tẽr), 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.