I was looking up a definition online, as I often do, in this case the British slang word tuppence; I got the standard "a slang reference to a coin denomination" definition from Wikipedia, but stumbled on these interesting ones given at The Urban Dictionary:
tuppence
Olden day word for a little girls [vagina]. Was once also slang word for money in ye olde england.
Fanny wiped her tuppence with a dish rag. Tally Ho.
Another word for a females Vagina.
A man has a winkle and a woman has a tuppence.
On one hand, those are two presumably independent contributors giving the same definition. On the other hand, you often can't trust The Urban Dictionary on some types of words, especially ones that have sexual meanings, because it's titillating for some people to give outrageous sexual definitions.
Some my questions are: Are the definitions given by these two correct? If so, what's the thinking behind the term?
Best Answer
I don't know if you can call this answer "masterful," but here goes.
This article (entitled: "Snatch," "Hole," or "Honey-pot"? Semantic Categories and the Problem of Nonspecificity in Female Genital Slang.) is quite an extensive study on many, many statistical phenomena and anomalies when it comes to, as they call it, female genital slang. They also compare these slang Female Genitalia Terms (FGTs) by category to Male Genitalia Terms (MGTs).
This article is very extensive, so to highlight what they have to say about the term "tuppence" (which here falls under the "money" category):
Thus, as @Garet Claborn intimated, this term seems to derive from referring to prostitutes, specifically cheap ones, and as they say points to women's worth (at least the opinion of the times) being in their genitalia.
With reference to your mention of whether or not this word enjoys usage, as you say a quick Google search will yield a number of hits connecting the word "tuppence" to a female genitalia reference. As for how widespread it is, a discussion on this forum suggests that it's not a very widespread and widely known word, one user saying the following:
Hope this answers your question.