topless (adj.)youdaoicibaDictYouDict[topless 词源字典]
of women, "bare-breasted," 1966, from top (n.1) + -less. Earlier it was used of men's bathing suits (1937) and women's (1964). Earliest sense is "without a visible summit; immeasurably high" (1580s).[topless etymology, topless origin, 英语词源]