I thought I knew what the word tart meant until someone learning English asked how the term ‘ tart’ could refer to a pastry filled with somethng sweet like jam, and yet when used as an adjective, referred to something sour.
According to the Oxford English Dictionary, the term tart dates from about 1400, and seems to be of French origin, when it seemed to refer to both sweet and savoury dishes, which tended to be open and could include bish, fowle, cheese, or fruit. From about the 18th century, it came to refer more to a sweet dish, with the traveller Celia Fiennes recording a West Country tart of apple with custard on top, so it seems ot have allowed other toppings to be added. It is possible that, as sugar was a luxury at the time, that for many years what we consider to be sweet were anything but, hence tarts were tart.
Some years ago I read a Victorian diary in which the author, a working class lad mentioned he was going out with a tart, which rather surprised me as he had seemed to be quite a respectable chap, hence the diary. When I read on I discovered it was a term of endearment, whereas I had always thought the term was derogatory.
According to the O E D, it is a term of endearment for the lower classes, especially in London, but also Liverpool, and exported to Australia and New Zealand. In 1959 children used the term widely with no sense of disrespect, in fact they often used the term ‘posh tart’ to distinguish the better classes, but it is the association with the lower orders that made the term lose its prestige.
It seems the term became applied to prostitutes from the late 19th century, by people in authority, hijacked if you like from its original meaning. Or perhaps there was always an association between working girls and working girls. This is not unusual, and suggests a huge social gap between the two users. In Indonnesian, the term ‘bung’ is a term of endearment, meaning brother, but in Australia it is a racist insult. The tonsure of monks went the other way – Romans persecuting them would shave their heads so monks took to shaving their own heads as a mark of pride.
From the 1930s its meaning shifted again, to refer to a young male prostitute, and seems to have held this meaning into the 1970s.