Lambdacism is the unconventional use of the symbol or sound represented in English by the letter L.
This is sometimes a matter of the custom - some natives of the British town of Bristol sometimes put an unexpected L sound at the ends of words: pianol or bananal, or even drawling (drawing) - or it may happen because someone whose native language doesn't have an R sound is speaking one that does: flied lice.
Other kinds of lambacism involve doubling the letter L in words that are usually spelled with one (which means that from an American perspective everyone who uses British English spelling does this all the time with words like travelling).
Lambacism can also involve putting a Y sound after a double L. This would turn The Mill on the Floss into The Mill yon the Floss, but I've never come across anyone who did this, myself.
Word To Use Today: lambdacism. The Greek letter that corresponds to the Roman letter L is called lambda, but for some reason the Romans called the habit of using Ls non conventionally labdacismus. Our English word has put back the Greek M.