"pressed close together, compacted in regular lines," 1667 (in "Paradise Lost"), probably a past-participle adjective from serry "to press close together" (1580s), a military term, from French serre "close, compact" (12c.), past participle of serrer "press close, fasten," from Vulgar Latin *serrare "to bolt, lock up," from Latin sera "a bolt, bar, cross-bar." It would be a parallel verb, based on a noun, to classical Latin serere "attach, join; arrange, line up," and, presumably, like it, from PIE root *ser- (2) "to line up."
Later use of serried is due to Scott, who linked it with phalanx.
The stubborn spearmen still made good
Their dark impenetrable wood,
Each stepping where his comrade stood,
The instant that he fell.
No thought was there of dastard fight ;
Link'd in the serried phalanx tight,
Groom fought like noble, squire like knight,
As fearlessly and well ;
[from "Marmion: A Tale of Flodden Field"]
updated on May 29, 2022