Etymology From Middle English dethlich, from Old English dēaþlīċ, equivalent to death + -ly.
1
Appearing as though dead, or on the verge of death.
He has a deathly pallor.
I rushed towards her, and embraced her with ardour; but the deathly languor and coldness of the limbs told me, that what I now held in my arms had ceased to be the Elizabeth whom I had loved and cherished.1816 June – 1817 April/May (date written), [Mary Shelley], chapter VI, in Frankenstein; or, The Modern Prometheus. […], volume III, London: […] [Macdonald and Son] for Lackington, Hughes, Harding, Mavor, & Jones, published 1 January 1818, →OCLC, page 120:
Etymology From Middle English dethlich, from Old English dēaþlīċ, equivalent to death + -ly.
1
In a way that resembles death.
He was deathly pale.
2
Extremely, dreadfully.
The water was deathly cold.
He was deathly afraid of crocodiles.
1 more example
And indeed, [Sydney] Sweeney’s quotes are deathly dull. On changing her body for “Christy,” she said: “It’s so fun just not being yourself.”2025 December 21, Esther Zuckerman, “Is Sydney Sweeney Today’s Most Perplexing Movie Star?”, in The New York Times, New York, N.Y.: The New York Times Company, →ISSN, →OCLC: