deadly

Etymology

From Middle English dedly, dedlych, dedlich, from Old English dēadlīċ (adjective); corresponding to dead + -ly. Cognate with Dutch dodelijk, German tödlich. The adverb is from Middle English dedliche, from Old English dēadlīċe (adverb), from the adjective.

adj

1. (obsolete, rare) Subject to death; mortal.
   […]he ſuffred hym ſelfe to be made mortall and dedly, that innocent & gyltles in hym ſelfe: he myght be ſlayne & deye for the gylty man. 1541, Rychard [W]hitforde, [D]yuers holy inſtrucyons and teachynges very neceſſarye for the helth of mannes ſoule[…], London: [W]yllyam Myddylton, page 36
   ❧ That when the iournay / of this dedly life / My ſely ghoſte / hath finiſhed and thence[…] 1545, [T]woo fruitfull and godly praiers, London: Rycharde Lante and Rycharde Bankes, page 36
   And next we find / Ourselves in Heaven. Even man's deadly life / Can be there, by God's leave. 1845, Phillip James Bailey, Festus: A Poem, Boston: Benjamin B. Mussey, page 270
2. Causing death; lethal.
3. Aiming or willing to destroy; implacable; desperately hostile.
   deadly enemies
4. Very accurate (of aiming with a bow, firearm, etc.).
   Its deadly aim at vast distances, which condition of the mechanical power brought has made it the dread of the sepoys, who term it "the gun that kills without making any sound," contrasts strangely with the performances of Brown Bess of old, which at any range beyond a hundred yards was so uncertain in its aim that it has been calculated that the soldier shot away the weight in lead of every man that he hit. 1858, “Woolwich Arsenal”, in The Living Age, volume 57, page 201
   For him the gibbet shall be built; For him the stake prepared: Him shall the scorn and wrath of men Pursue with deadly aim ; And malice, envy, spite and lies, Shall desecrate his name. 1859, Iowa Instructor - Volume 1, page 110
   Slaves have been freed, religious tests revoked, Bread tax abolished, and free trade secured, Reform twice carried, franchise much enlarged, With deadly aim to crush foul bribery, And promise given of yet better things. 1869, George Swann, The Autumn Wreath: A Selection of Original Poetry, page 92
   Possibly some have thought that we were going to make war on some favorite doctrine or political dogma; that we had set brethren to whetting their sword, and drawing their bow for deadly aim at precious truth; as the wicked Haman had secured a decree that all the Jews should be killed. 1888, Annual Session of the Baptist Congress for the Discussion of Current Questions, page 188
   The Elf turned and with deadly accuracy shot an arrow where his nose pointed him. The shaft sliced through the air, pierced the tall grass, and struck the Dwarf's shoes one hundred yards out . . . but the Dwarf was not in them! 2006, Gene Del Vecchio, The Sword of Anton, page 51
   Was that really her mom grabbing a large Nerf gun from some sort of side holster and aiming it straight at Camden's head? Yes, it was. And the woman was blessed with deadly accuracy. 2015, Melody Anne, Her Unexpected Hero, page 288
   There is a wealth of common sense and humanity in that, and perhaps the most unexpected element in the idea of the Seven Deadly Sins is that, although it points with deadly accuracy to our capacity for evil, it also leaves us with a vivid and strong sense of what it means to be human. 2015, Henry Fairlie, The Seven Deadly Sins Today
5. (informal) Very boring.
   Now, at school, I was forced to sit in classes, to take notes and exams, to use textbooks that were flat, impersonal, deadly. 2001, Oliver Sacks, Uncle Tungsten: Memories of a Chemical Boyhood
   Students, of course, know the difference between a deadly lecture and a stimulating one. An excellent lecturer who maintains a high level of interaction with the audience stimulates thinking and learning. 2009, Gay Lumsden, Donald Lumsden, Carolyn Wiethoff, Communicating in Groups and Teams: Sharing Leadership, page 324
6. (informal, Australian Aboriginal, Ireland, Newfoundland) Excellent, awesome, cool.

adv

1. (obsolete) Fatally, mortally.
2. In a way which suggests death.
   Her face suddenly became deadly white.
3. Extremely, incredibly.
   Though deadly weary, till ſpectators do / At once part and call them good boys too[…] 1669, Roger Boyle, 1st Earl of Orrery, “Tryphon, A Tragedy”, in Two New Tragedies: The Black Prince, and Tryphon[…], page iv
   John had got an impreſſion that Lewis was ſo deadly cunning a man, that he was afraid to venture himſelf alone with him. 1750 [1712], John Arbuthnot, “The Hiſtory of John Bull (chapter XVIII)”, in The Hiſtory of John Bull and Poems on ſeveral Occaſions[…], page 113