One of my favorite linguistic phenomena is rebracketing, which is when a word or words is/are redivided differently, either two words becoming one, one word heard as two, or part of one word interpreted as part of the other. This frequently happens with articles, for example:
apron was originally napron, but “a napron” was interpreted as “an apron”
newt comes from ewt by the same process
In the opposite direction, nickname comes from Middle English nekename which in turn came from ekename (an ekename -> a nekename) where “eke” was an old word meaning “also” or “additional” (so basically “an additional name”)
ammunition comes from an obsolete dialectal French amunition, which came from munition, the phrase la munition being heard as l’amunition.
the nickname Ned comes from Ed, via “mine Ed” being heard as “my Ned” (in archaic English, “my” and “mine” had the same relationship as “a” and “an”), same with several other nicknames like Nell
The word “orange” ulimately derives from the Arabic nāranj, via French “orange”, the n being lost via a similar process involving the indefinite article, e.g., something like French “une norange” becoming “une orange” (it’s unclear which specific Romance language it first happened in)
in the Southern US at least (not sure about elsewhere), “another” is often analyzed as “a nother”, hence the phrase “a whole nother”
omelet has a whole series of interesting changes; it comes from French omelette, earlier alemette (swapping around the /l/ and /m/), from alemelle from an earlier lemelle (la lemelle -> l’alemelle)
Related to this, sometimes two words, especially when borrowed into another language, will be taken as one. Numerous words were borrowed from Arabic with the definite article al- attached to them. Spanish el lagarto became English alligator. An interesting twist is admiral, earlier amiral (the d probably got in there from the influence of words like “administer”) from Arabic amir al- (lord of the ___), particularly the phrase amir al-bahr, literally “lord of the sea”.
Sometimes the opposite happens. A foreign word will look like two words, or like a word with an affix. For example, the Arabic kitaab (book) was borrowed into Swahili as kitabu. ki- happens to be the singular form of one of the Swahili genders, and so it was interpreted as ki-tabu. To form the plural of that gender, you replace ki- with vi-, thus, “books” in Swahili is vitabu. The Greek name Alexander became, in Arabic, Iskander, with the initial al- heard as the article al-.
Similarly, the English word Cherry came from Old Norman French cherise, with the s on the end interpreted as the plural -s. Interestingly enough, that word came from Vulgar Latin ceresia, a feminine singular noun, but originally the plural of the neuter noun ceresium! So a Latin plural was reinterpreted as a singular in Vulgar Latin, which in turn was interpreted as a plural when borrowed into English!
The English suffix -burger used with various foods (e.g., cheeseburger, or more informally chickenburger, etc.) was misanlyzed from Hamburger as Ham-burger, itself from the city of Hamburg
This can happen even with native words. Modern French once is used for the snow leopard, but originally meant “lynx”. In Old French, it was lonce (ultimately from the same source as lynx), which was reinterpreted as l’once! In English, the word “pea” was originally “pease”, but that looked like it had the plural -s on it, and so the word “pea” was created from it. Likewise, the adjective lone came from alone, heard as “a lone”, but alone itself came originally from all one.
