%imbitter%

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. [ 1913 Webster ]

Is there anything that more imbitters the enjoyment of this life than shame? South. [ 1913 Webster ]

Imbittered against each other by former contests. Bancroft. [ 1913 Webster ]

n. One who, or that which, imbitters. [ 1913 Webster ]