The Spanish horno, for “oven,” sounds unrelated to any English counterpart.
But it is in fact a close cousin of furnace. Both come from the Latin formus, meaning “warn”.
How did such dissimilar words end up such close cousins?
Because most Latin words that began with an f- followed by a vowel ended up evolving in Spanish (alone among the romantic languages) into an h-. Thus the h‑r-n of horno maps almost exactly to the f‑r-n of furnace. In both cases, the original ‑m- evolved into an ‑n- in the root. But that is a very common transition too, with both sounds being so similar.
The Spanish “hablar” (“to talk”) comes from the vulgar Latin “fabulari”, also meaning, “to talk” — hence the English, “fable”.
This gets very interesting very quickly, so note:
The Spanish “Huir” comes from the same Latin root as “fugitive”, “fugitivus”, meaning, “to flee”.
Pattern: Latin words that began with an ‘F’ tended to lose that initial ‘F’ sound and became silent (yet represented in writing with an ‘H’) as vulgar Latin turned into Spanish.
From the Latin fundus (“bottom”), we get the Spanish fondo (“background”) and hondo (“deep”) — as well as the English profound. After all, when someone says something profound, well, that’s deep.
The mapping of the Spanish f‑n-d (or h‑n-d) to the English (pro)-f-n‑d is straightforward. However, it’s curious that, in hondo, the initial F transformed from Latin into Spanish to an initial H. This is a common pattern, unique to Spanish, that we see in many Latin words as they transformed into Spanish, such as hijo and filial, refuse and rehusar, and higado and fig.
If he is fuming, he is smoking — literally. And it is, subtly, the same word in Spanish.
“To fume” comes from the Latin root fumus (“smoke”) from which we also get the common Spanish word for “smoke”, humo. But they don’t sound alike, so how are they related?
The Spanish humo is a great example of the pattern of the Initial F turning into an H in Spanish, alone among the languages of the world. Many Latin words that began with an F, and come to us in English through the Latinate F form, became the equivalent word but with an H- in Spanish. Take hermano and filial, for example. Or fact and hecho.
Other English words from the same root fumus include fumigation (ahhhh!) and the less common fetid. Fetid is a dirty, Shakespearean word, after all.