Abarim Publications' online Biblical Hebrew Dictionary
The verb איב ('ayab) means to be hostile to or to be an enemy. This verb occurs in all expectable ways, from men being hostile to men (Numbers 35:23), to men treating men as enemies (Exodus 23:22), to a general or national enemy (Exodus 15:6), to enemies of God (Numbers 10:35). Most notable are the instances where God becomes the enemy of rebellious men (Isaiah 63:10).
This verb comes with one derivative: the feminine noun איבה ('eba), meaning enmity (Genesis 3:15, Numbers 35:21).