swagger (v.)

"move heavily or unsteadily," 1520s, now provincial or archaic, probably from a Scandinavian source akin to Old Norse sveggja "to swing, sway," from the same source as Old English swingan "to swing" (see swing (v.)). Earlier it meant "swing an object" (c. 1400), "swing or shake freely" (late 15c.). Related: Swagged; swagging (mid-15c.).

"blusterer; bully; boastful, noisy fellow," 1590s, agent noun from swagger (v.).

"stylish, classy, posh," 1913, from earlier noun or verb (see below); "A midland and s.w. dial. word taken into general slang use at the beginning of the 20th cent." [OED].

Swank (n.) "ostentatious behavior" is noted in 1854 as a Northampton word ("what a swank he cuts!"); swank (v.) is attested from 1809 as "to strut, behave ostentatiously."

Perhaps the group is ultimately from a Germanic root meaning "to swing, turn, toss" (source also of Middle High German swanken "to sway, totter, turn, swing," Old High German swingan "to swing;" see swing (v.)). If so, OED suggests (2nd ed. print, 1989), it is perhaps from the notion of "swinging" the body ostentatiously (compare swagger). Related: Swankpot "ostentatious or boastful person" (1914).

A separate swank word-thread in English is from Old English swancor "pliant, bending," also held to be from the swing root (compare German schwank "pliant," Old Norse svangr "thin, slender, slim"). From this comes a number of words now dialectal or obscure, such as swanky (n.) "active or clever young fellow" (c. 1500), also "small beer, weak fermented drink" (1841); swanking "supple, active."