To kill off is to destroy something completely. Kill off the character, killed off by competition, kill off the disease.
In drama it means writing a character out by killing them, which is what happens when an actor leaves. Of a species or a trade it means finishing what was already declining rather than a sudden end.
1phrasekill offTo destroy something completely.
“The new supermarket could kill off the small shops on the high street.”
kill off is a destroying.
Also accepted in games: wreck
Kill plus off, with off adding the sense of completion.
From kill + off.
Etymology from Wiktionary, CC BY-SA
Practised in Phrasal Verbs