1580s, Italian title of address or courtesy, equivalent to madam; from c. 1600 as a noun, "an Italian lady," from Italian madonna, from Old Italian ma donna (Italian mia donna) "my lady," from ma "my" + donna "lady," from Latin domina "lady, mistress of the house," from Latin domus "house" (from PIE root *dem- "house, household").
Often specifically "the Virgin Mary," hence the sense of "picture or statue of the Virgin Mary," attested in English by 1640s. The U.S. singer/dancer (full name Madonna Louise Ciccone, b. 1958) attained to pop stardom in the fall of 1984.
in music, "becoming gradually slower," 1811, from Italian, present participle of ritardare "to slow down," from Latin retardare "to make slow" (see retardation). The Italian plural is ritardandi.