2. Noun. (slang) A fragmentation grenade ¹
3. Verb. (US military slang) To deliberately kill (one's superior officer) with a fragmentation grenade. ¹
4. Verb. (video games slang) To kill (another player) in a deathmatch computer game. ¹
¹ Source: wiktionary.com
Definition of Frag
1. to injure with a type of grenade [v FRAGGED, FRAGGING, FRAGS]