Word Origin & History
O.E. side "flanks of a person, the long part or aspect of anything," from P.Gmc. *sithon (cf. O.S. sida, O.N. siða, M.Du. side, O.H.G. sita, Ger. Seite), from adj. *sithas "long" (cf. O.E. sid "long, broad, spacious," O.N. siðr "long, hanging down"), from PIE base *se- "long, late" (cf. L. serus
"late," Lith. sietuva "deep place in a river," M.Ir. sith, M.Breton hir "long"). Original sense preserved in countryside
. Fig. sense of "position or attitude of a person or set of persons in relation to another" (cf. choosing sides) first recorded mid-13c. Meaning "music on one side of a phonograph record" is first attested 1936. Phrase side by side "close together and abreast" is recorded from c.1200. Restaurant phrase on the side "apart from the main dish" is attested from 1884, Amer.Eng. Side-splitting "funny" is first attested 1860. Sidebar "secondary article in a newspaper" is recorded from 1948. Sideman "supporting musician" is first attested 1936. Sideboard "table placed near the side of a room" is from c.1300.
"to cut into sides" (of meat), c.1470, from side
(n.). Meaning "to support one of the parties in a discussion, dispute, etc.," is first attested 1591, from side
(n.) in the fig. sense; earlier to hold sides (c.1489).