deadly

(used as intensives) extremely.

“deadly dull”

“deadly earnest”

As if dead.

Causing or capable of causing death.

“a deadly enemy”

Involving loss of divine grace or spiritual death.

“the seven deadly sins”

Of an instrument of certain death.

“deadly poisons”

Extremely poisonous or injurious; producing venom.

Exceedingly harmful.

(of a disease) having a rapid course and violent effect.