steyǵʰ-mn̥-
“stepped path, ascending way”stile, stair, stich, distich
Nominal of *steyǵʰ- giving English stile, stair, Greek stikhos > stich, distich.
Discussion
The PIE form *steyǵʰ-mn̥- (stepped path, ascending way) derives from the verbal root *steyǵʰ- (to step, to stride, to ascend), with the result noun suffix *-mn̥-. The literal meaning is "the thing stepped" — a path defined by the act of climbing it, an ascending way.
The Germanic branch preserves the root most transparently. English stair (OE stǣger, from PGmc *staigriz) continues the root with the expected consonant shifts: PIE *st- > PGmc *st- (unchanged), PIE *ǵʰ > PGmc *g. The related words stile (OE stigel, a stepped crossing over a fence), stile (as in turnstile), and the archaic sty (to ascend, as in "sty up the mountain") all continue the stepping/climbing sense.
German steigen (to climb, to rise) and Steig (a steep path) preserve the verbal and nominal forms directly. The German compound Steigbügel (stirrup, literally "climbing-bow") names the riding equipment by its function: the thing you step into to mount a horse.
Greek steíkhein (στείχειν, "to walk, to march in rows") preserves the root with a subtly different emphasis — not climbing but ordered walking, marching in formation. The derivative stíkhos (στίχος, "row, line, verse of poetry") gave English stich (a line of verse) and distich (a couplet, two lines). The connection between stepping and versification is the concept of measured progression: a line of poetry is a measured step, a verse is a turned step (Latin versus, from vertere, but the metaphor of feet in poetry uses the same ambulatory imagery).
Old Irish tíagu (I go) and the related forms confirm the Celtic reflexes. Sanskrit stighnoti (he ascends) provides Indo-Iranian attestation.
The root occupies an interesting conceptual niche in the PIE motion vocabulary. Where *gʷem- meant "to come/arrive" and *h₃ey- meant "to go/journey," *steyǵʰ- specifically meant upward movement — climbing, ascending, mounting. The specialisation of a root for specifically vertical locomotion implies an environment where ascending was a distinct and frequent activity: hills, slopes, mounted animals, or defensive walls.