Synonyms for Deathly:

adj.

•cadaverous (adjective)
ghostly.
•fatal (adjective)
mortal, deadly.
•suggesting end of life (adjective)
deathlike, pale, ghastly, gaunt, cadaverous.

n.

death throes, death, dying, mortality, morbidity, fatality, bereavement, death toll, death rate, demise. •deathlike (noun)
dull, pale, ghastly, gaunt, cadaverous.
•deathly (noun)
deadly, mortal, fatal, deathlike, dead.

Other synonyms:

ghostlike. spectral, cadaverous. ghostly. ghastly.

Usage examples for deathly

1. Yet the deathly cold was giving way like ice before the sun. – The Safety Curtain, and Other Stories by Ethel M. Dell

2. I don't shoot, you know; it's deathly enough as it is. – The Firing Line by Robert W. Chambers