1.
see kill 3
2.
If you say that a group or an amount of something has been killed off, you mean that all of them or all of it have been killed or destroyed.
Their natural predators have been killed off...
It is an effective treatment for the bacteria and does kill it off...
All blood products are now heat treated to ~ any infection.
PHRASAL VERB: be V-ed P, V n P, V P n (not pron)