Late 17th century (in an earlier sense). From post-classical Latin rossalia, also rosalia, apparently from Italian rosalia (although this is apparently first attested later: 1585, but see note), probably an alteration (with suffix substitution; compare -ale) of rosolia measles from rosa + a suffix of uncertain origin (perhaps compare -olo, diminutive suffix: see -ule) + -ia.

Late 18th century; earliest use found in Thomas Busby (1754–1838), composer and author. Apparently from Italian Rosalia, probably from French rosalie, apparently ultimately from the female forename Rosalie, Rosalia.