Dimwell Arrhythmic Rhyming Slang
In rhyming slang, a common word is replaced with a short, rhyming phrase, and then the original rhyming word is omitted ("hemiteleia"), making the origin of the phrase elusive to people unfamiliar with the use. A typical roundworld example is to refer to "stairs" as "apples", contracted from "apples and pears"
Dimwell Arrhythmic Rhyming Slang (DARS) is the only rhyming slang, anywhere, that does not rhyme and in fact is very carefully devised to avoid creating any rhyme, rhythm, alliteration, internal or external assonance, or anything even remotely resembling or which might be mistaken for poetic structure. As with all rhyming slang, it has been speculated that this is mainly to annoy or confuse outsiders (Cryptolect, or Cant) Dimwell people are just doing it better than anyone else. Or alternatively it is not carefully devised, it's just that Dimwell is aptly named.
"Wig" in DARS is "Prunes", as in "Syrup of Prunes" (in the Cockney rhyming slang of Roundworld, "Wig" is "Syrup, as in "Syrup of Figs" - unlike Dimwell, in this version it is clear which word has to be dropped)
"Cup and plate" - No definition, but means "not right" as in "he's a bit cup-and-plate in the head.
"Plates of meat" - no definition, but means "Kippers"
A prominent speaker is Tolliver Groat, the current Deputy Postmaster.
Dimwell Arrhythmic Rhyming Slang is of course based on the venerable Cockney Rhyming Slang, a similar highly localised dialect of a major city which, while always rhyming with the original word, can be just as impenetrable to the uninitiated. Particularly of note is that a single word normally becomes two or three words (normally the words relate to each other somehow but seldom in the same way each time) , but while the cockney slang phrase for a word always rhymes, mostly speakers don't actually use the full phrase, they shorten it to a single word which is always the non-rhyming word thus meaning that in practice the rhyme is almost always lost when spoken. For example; the cockney for 'mouth' is 'north and south' but a cockney would say 'his north opened'.
From the few examples we have, Dimwell slang seems to take what would have been rhyming slang and change one word to eliminate the rhyme; thus, a common phrase such as "cup and spoon" might have indicated "a loon" but to eliminate the rhyming clue, "spoon" was changed to "plate".
While DARS doesn't share the rhyming routes of its Roundworld counterpart, when spoken out loud the two would in fact make about as much sense to anyone who hadn't come across it before, but at the very least you have to credit DARS for being more honestly named and being famous for just messing with the non-locals.