imbitter \imbit"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.
   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
see also:
imbittered imbittering embitter embitter