Adder, apron and umpire all used to start with an “n”. Constructions like “A nadder” or “Mine napron” were so common the first letter was assumed to be part of the preceding word. Linguists call this kind of thing reanalysis or rebracketing.
Wasp used to be waps; bird used to be brid and horse used to be hros. Remember this when the next time you hear someone complaining about aks for ask or nucular for nuclear, or even perscription. It’s called metathesis, and it’s a very common, perfectly natural process.
English spelling can be a pain, but it’s also a repository of information about the history of pronunciation. Are we being lazy when we say the name of the third day of the working week? Our ancestors might have thought so. Given that it was once “Woden’s day” (named after the Norse god), the “d” isn’t just for decoration, and was pronounced up until relatively recently. Who now says the “t” in Christmas? It must have been there at one point, as the messiah wasn’t actually called Chris. These are examples of syncope.
Our anatomy can make some changes more likely than others. The simple mechanics of moving from a nasal sound (“m” or “n”) to a non-nasal one can make a consonant pop up in-between. Thunder used to be “thuner”, and empty “emty”. You can see the same process happening now with words like hamster, which often gets pronounced with an intruding “p”. This is a type of epenthes
A dark “l”, in linguistic jargon, is one pronounced with the back of the tongue raised. In English, it is found after vowels, as in the words full or pole. This tongue raising can go so far that the “l” ends up sounding like a “w”. People frown on this in non-standard dialects such as cockney (“the ol’ bill”). But the “l” in folk, talk and walk used to be pronounced. Now almost everyone uses a “w” instead- we effectively say fowk, tawk and wawk. This process is called velarisation.
Your grandmother might not like the way you pronounce tune. She might place a delicate “y” sound before the vowel, saying tyune where you would say chune. The same goes for other words like tutor or duke. But this process, called affrication, is happening, like it or not. Within a single generation it has pretty much become standard English.
Borrowing from other languages can give rise to an entirely understandable and utterly charming kind of mistake. With little or no knowledge of the foreign tongue, we go for an approximation that makes some kind of sense in terms of both sound and meaning. This is folk etymology. Examples include crayfish, from the French écrevisse (not a fish but a kind of lobster); sparrow grass as a variant for asparagus in some English dialects; muskrat (conveniently musky, and a rodent, but named because of the Algonquin word muscascus meaning red); and female, which isn’t a derivative of male at all, but comes from old French femelle meaning woman.
English spelling can be a pain. That is mainly because our language underwent some seismic sound changes after the written forms of many words had been more or less settled. But just to confuse matters, spelling can reassert itself, with speakers taking their cue from the arrangement of letters on the page rather than what they hear. This is called spelling pronunciation. In Norwegian, “sk” is pronounced “sh”. So early English-speaking adopters of skiing actually went shiing. Once the rest of us started reading about it in magazines we just said it how it looked. Influenced by spelling, some Americans are apparently starting to pronounce the “l” in words like balm and psalm (something which actually reflects a much earlier pronunciation).