deathly (adj.)

Old English deaþlic "mortal, subject to death" (a sense now obsolete); see death + -ly (1). Meaning "deadly" (of poison, sin, etc.) is from c. 1200; that of "death-like, characteristic of death, resembling death" is from c. 1200, originally of complexion. Compare deadly. Related: Deadliness.

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Definitions of deathly from WordNet
deathly (adv.)
to a degree resembling death;
he was deathly pale
deathly (adv.)
to an extreme degree;
the night was deathly cold
as a child, I was deathly afraid of snakes
Synonyms: extremely / exceedingly / super
deathly (adj.)
having the physical appearance of death;
a deathly pallor
Synonyms: deathlike
deathly (adj.)
causing or capable of causing death;
Synonyms: deadly / mortal