frag vs rub out

frag

verb
  • To kill. 

  • To hit with the explosion of a fragmentation grenade. 

  • To deliberately kill (one's superior officer) with a fragmentation grenade. 

  • I fragged him but he fell off the ledge afterwards. 

noun
  • A successful kill in a deathmatch game. 

  • A fragmentation grenade. 

rub out

verb
  • To kill, especially to murder. 

  • To delete or erase or remove (something) by rubbing. 

How often have the words frag and rub out occurred in a corpus of books? (source: Google Ngram Viewer )