rugae n.

"watercourse, dry stream bed," 1845, a California word, from American Spanish, in Spanish, "rivulet, small stream," perhaps from Latin arrugia "shaft or pit in a gold mine," which is apparently a compound of ad "to" (see ad-) + ruga "a wrinkle" (see rugae).

"to wrinkle, to draw or contract into folds," 1610s, from Latin corrugatus, past participle of corrugare "to make full of wrinkles, wrinkle very much" (also "produce loathing, cause disgust"), from assimilated form of com-, here perhaps an intensive prefix (see com-), + rugare "to wrinkle," from ruga "crease, groove," which is of uncertain origin (see rugae).

French for "street," from Vulgar Latin *ruga (source also of Old Italian ruga, Spanish rua "street in a village"), from Latin ruga, properly "a furrow," then in Medieval Latin "a path, street," (see rugae).