Although the ultimate origin of slut is unknown, it first appeared in Middle English in 1402 as slutte (AHD), with the meaning "a dirty, untidy, or slovenly woman." Even earlier, Geoffrey Chaucer used the word sluttish (c.1386) to describe a slovenly man; however, later uses appear almost exclusively associated with women. The modern sense of "a sexually promiscuous woman" dates to at least 1450.
Another early meaning was "kitchen maid or drudge" (c. 1450), a meaning retained as late as the 18th century, when hard knots of dough found in bread were referred to as "slut's pennies." A notable example of this use is Samuel Pepys's diary description of his servant girl as "an admirable slut" who "pleases us mightily, doing more service than both the others and deserves wages better" (February 1664). In the 19th century, the word was used as a euphemism in place of bitch in the sense of "a female dog."
Similar words appear in Dutch, German and Swedish dialects meaning "a dirty woman," indicating a common ancestor in Germanic languages. The word entered the colloquial Yidish as "akhsluttishkha" meaning "a hag". It exists in Ukrainian too as slutyj as a loan word from Yidish or via the mediaeval Scandinavian Varangian colonists in Kievan Rus'. A popular theory connects slut to earlier Germanic forms meaning "slush" or "mud puddle," but this derivation remains in question.
The accepted denotative meaning is a sexually promiscuous woman or "a woman of a low or loose character; a bold or impudent girl; a hussy, jade. These definitions identify a slut as a person of low character — a person who lacks the ability or chooses not to exercise a power of discernment to order their affairs, such as a cad, rake, or womanizer. The adjective "slutty" carries a similar connotation but can be applied both to people and to clothing and accessories, such as Halloween costumes.
The term slut is therefore frequently used as an insult. The derogatory power of the term derives both from its denotative meaning of a promiscuous woman, but also from its historical and regional connotations or alternate meanings that identify a slut as a dirty or unkempt person. These additional meanings and connotations are negative and identify a slut as being a slovenly and ugly person, for example as in these quotations from OED2:
The British journalist Katharine Whitehorn attempted to re-claim this latter meaning in a famous 1963 article in The Observer: "Have you ever taken anything out of the dirty-clothes basket because it had become, relatively, the cleaner thing? Changed stockings in a taxi? Could you try on clothes in any shop, any time, without worrying about your underclothes? How many things are in the wrong room—cups in the study, boots in the kitchen? ... [this makes] you one of us: the miserable, optimistic, misunderstood race of sluts." This article prompted a flurry of correspondence, with many women writing in to describe their own acts of sluttishness.
With BDSM, polyamorous and non-monogamous people, in usage taken from the book The Ethical Slut, the term has been reclaimed as an expression of choice to openly have multiple partners, and revel in that choice: "a slut is a person of any gender who has the courage to lead life according to the radical proposition that sex is nice and pleasure is good for you. A slut is a person who has taken control of their sexuality and has sex with whomever they choose, regardless of religious or social pressures or conventions to conform to a straight-laced monogamous lifestyle committed to one partner for life. The term has been "taken back" to express the rejection of the concept that government, society, or religion may judge or control one's personal liberties, and the right to control one's own sexuality.
A few porn stars have embraced the term as a badge of pride for a sex-positive person.
The term is also used (principally by women) to describe a woman dressed provocatively or a woman being overtly flirtatious.