death·ly I. \ˈdethlē, -li\adjective Etymology: Middle English dethlich deadly, mortal, from Old English dēathlīc mortal, from dēath death + -līc -ly 1.: deadly, fatal, mortal, destructive 2.: like or having the characteristics of death < a deathly stillness > 3.: of, relating to, or suggestive of death < I marked each deathly change in him — Robert Browning > Synonyms:see deadly II. adverb : in a way or to a degree resembling or approximating death < deathly sick >