Origin and history of swell

Middle English swellen, from Old English swellan "grow in bulk, become bigger" (intransitive, past tense sweall, past participle swollen), from Proto-Germanic *swellanan, *swallejanan (source also of Old Saxon swellan, Old Norse svella, Old Frisian swella, Middle Dutch swellen, Dutch zwellen, Old High German swellan, German schwellen "make swell"), which is of unknown origin. "Most likely a substratum etymon" [Boutkan].

By c. 1200 as "move or spread upward" (of the sea, etc.), also "become markedly enlarged." In reference to shape, "protuberate, bulge out, belly," as a sail in the wind or the middle of a cask, from 1670s.

In reference to emotions, pride, etc., "rise and grow," from late 14c.; of music from 1749. Transitive sense, "make larger in bulk" (also size, amount, number of) is from c. 1400. Related: swelled; swollen; swelling.

c. 1200, swelle, in medicine, "a morbid swelling," from swell (v.). In reference to a rise or long unbroken wave of the sea, it is attested from c. 1600 (earlier of rivers). In reference to ground, "an elevation above a level," by 1764, with more specific sense in geology. Of music (or other sounds), "gradual increase and subsequent decrease in loudness or force," by 1757.

The meaning "wealthy, elegant or fashionable person" ["A man of great claims to admiration" - Century Dictionary] is attested by 1786, likely an image of visibly puffed-up demeanor or behavior. It also implied "person who puts on airs, a mere dandy;" compare now-obsolete swell (n.) "pompousness, arrogance" (1724).

Thence Thackeray's swelldom "the realm of swells" (1855); swell-mob (1836) "class of pickpockets who go about dressed genteely, the better to mingle unsuspected."

1810, of persons, "fashionably dressed or equipped," from swell (n.) in the "stylish person" sense. Of things, "stylish, elegant," by 1812. In a broader sense of "good, excellent, first-rate of its kind," by 1897; in a weakened sense of "very good" by 1926. Swell as an interjection of satisfaction is recorded by 1930 in American English. Middle English swelle (adj.) meant "proud, arrogant" (c. 1400).