deadly Definition

deadly
adj deadlier, deadliest

1. Causing or likely to cause death.

Thesaurus: fatal, lethal, murderous, mortal, homicidal, destructive, deleterious, malignant, baneful, injurious; Antonym: healthful, reviving, beneficial.
2. colloq
Very dull or uninteresting.
Thesaurus: tiresome, boring, tedious, dull, uninteresting, monotonous, wearisome.
3. Very great.

Example: in deadly earnest

adverb

1. Very; absolutely.

Derivative: deadliness
noun