Internecine (adjective)

Characterized by or involving mutual slaughter or destruction; deadly to both sides.

Origin:

Late 16th century, from latin internecinus 'deadly to both sides', from inter- 'between' + necare 'to kill'.

Examples:

1. The internecine war between the two factions lasted for years.
2. The internecine conflict caused widespread suffering.
3. The internecine struggle for power left the country in ruins.
4. The internecine fighting was brutal and unrelenting.
5. The internecine rivalry between the two companies was vicious.