acerbity, acid, acidity, acidulousness, acrimony, animosity, animus, asperity, bad blood, bad feeling, bile, bitter feeling, bitter resentment, bitterness, bitterness of spirit, causticity, choler, disaffinity, feud, gall, gnashing of teeth, hardheartedness, heartburning, hostility, ill blood, ill feeling, ill will, immediate dislike, personality conflict, rancor, rankling, slow burn, soreness, sourness, spleen, vendetta, venom, virulence, vitriol