rancorous (adj.)

• acerb
• acerbic
• acid
• acidic
• acidulent
• acidulous
• acrid
• acrimonious
• antagonistic
• antipathetic
• belligerent
• bitter
• burning
• caustic
• choleric
• clashing
• conflicting
• despiteful
• evil
• hateful
• hostile
• implacable
• irreconcilable
• malevolent
• malicious
• malign
• malignant
• punitive
• punitory
• quarrelsome
• repugnant
• resentful
• retaliatory
• revengeful
• sore
• spiteful
• splenetic
• unappeasable
• vengeful
• venomous
• vicious
• vindicatory
• vindictive
• virulent
• vitriolic
• wicked