"last resource, what one would do at the worst," 1670s, French, literally "to go worse," from pis "worse," from Latin peius, neuter of peior "worse" (see pejorative) + aller "to go" (see alley (n.1)).
Entries linking to pis aller
pejorative adj.
"depreciative, disparaging, giving a low or bad sense to," 1888, from French péjoratif, from Late Latin peiorat-, past-participle stem of peiorare "make worse," from Latin peior "worse," perhaps originally "stumbling," from PIE *ped-yos-, suffixed (comparative) form of *ped- "to walk, stumble, impair," from root *ped- "foot." As a noun, "a word that depreciates the sense," from 1882. English had a verb pejorate "to worsen" from 1640s.
alley n.1
mid-14c., "passage in a house; open passage between buildings; walkway in a garden," from Old French alee (13c., Modern French allée) "a path, passage, way, corridor," also "a going," from fem. of ale, past participle of aler "to go," which is of uncertain origin. It might be a contraction of Latin ambulare "to walk" (Watkins, see amble (v.)), or it might be from Gallo-Roman allari, a back-formation from Latin allatus "having been brought to" [Barnhart]. Compare sense evolution of gate.
Applied by c. 1500 to "long narrow enclosure for playing at bowls, skittles, etc." Used in place names from c. 1500. "In U.S. applied to what in London is called a Mews" [OED], and in American English especially of a back-lane parallel to a main street (1729). To be up someone's alley "in someone's neighborhood" (literally or figuratively) is from 1931; alley-cat (n.) is attested by 1890.