i Register
In some senses, thwack is marked as figuratively, obsolete. Watch for register when choosing this word.
verb
To hit (someone or something) hard, especially with a flat implement or a stick; to thrash, to whack.
This carter thwacketh his horse upon the croup, / And they began to drawen and to stoop.
Flaies lustily thwack, / least plough séede lack.
To drive or force (someone or something) by, or as if by, beating or hitting; to knock.
But let him ſvveare ſo, and he ſhall not ſtay, / VVee'l thvvack him hence vvith Diſtaffes.
To pack (people or things) closely together; to cram.
[W]hen hee comes to deſcribe the office of his imaginarie doctor [he] thvvacks fourteene Scriptures into the margent, vvhereof not any one hath any iuſt colour of inference to his purpoſe: […]
[W]ho vvould have thought a man could have thvvackt together ſo many incongruous ſimilitudes, had it not been to defend the motley i[n]coherence of a patch'd Miſſall?
To decisively defeat (someone) in a contest; to beat, to thrash.
3 [Servingman] VVhy here's he that vvas vvont to thvvacke our Generall, Caius Martius. / 1 VVhy do you ſay, thvvacke our Generall? / 3 I do not ſay thvvacke our Generall, but he vvas alvvayes good enough for him.
[W]hat adventurous knight ever thought of the lady's terror, when he went to thwack giant, dragon, or magician, in her presence, and for her deliverance?
To crowd or pack (a place or thing) with people, objects, etc.
And my lad Aſcanius with a Troian mantel adorning, / Weau'd woorks thwackt with honor, to her gifts this parlye ſhe lincketh.
noun
An act of hitting hard, especially with a flat implement or a stick; a whack; also, a powerful stroke involved in such hitting; a blow, a strike.
Him Ralph encountred, and straight grew / A fierce Dispute betwixt them two: / Th'one arm'd with Metall, t'other with Wood; / This fit for bruise, and that for Blood. / With many a stiff thwack, many a bang, / Hard Crab-tree and old Iron rang; / While none that saw them could divine / To which side Conquest would encline: […]
Noble Captain, Lend a reaſonable Thvvack, for the Love of God, vvith that Cane of yours, over theſe poor Shoulders.
A dull or heavy slapping sound.
I had scrambled out of the coach, and was instinctively settling my cravat, when somebody brushed roughly by me, and I heard a smart thwack upon the coachman’s ear. […] And then came a second thwack, aimed at the driver's other ear, but which missed it, and hit him on the nose, causing a terrible effusion of blood.
"It's a comfort they're most on'em females," he pursued, sounding a thwack on his knee as he settled himself agreeably in his seat.
intj
Used to represent the dull or heavy sound of someone or something being hit or slapped.
Three watrie clowds ſhymring toe the craft they rampired hizzing, / Three whern's fierd gliſtring, with ſouthwynds rufflered huffling. / Now doe they rayſe gaſtly lightnings, now griſlye reboundings / Of ruffe raffe roaring, mens harts with terror agryſing. / With peale meale ramping, with thwick thwack ſturdilye thundring.
And then—Thwack! Anne had brought her slate down on Gilbert's head and cracked it—slate, not head—clear across.