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.
The Spanish huso (“spindle” — what Cinderella uses to weave!) comes from the Latin for the same: fusus.
The transition is clear when we remember that the initial F in Latin usually turned into an “h” in Spanish: fig vs higo, for example. Or herir vs interfere, for another.
From the same Latin root fusus, we also get the English… fuse. Why? Well, look at the shape: an old-school spindle looks like a big fuse!
Thus, we can see the f‑s of fuse map clearly to the h‑s of huso.
The Spanish hilo (cord; thread; string) comes from the Latin for the same, filum. The words sound very different, until we remember that, words in Latin that began with a f- tended to change to h- in Spanish: hijo/filium, and hoja/foliage, for example. Now the hilo/filum make sense!
Interestingly, however, from that same Latin root filum, we get various English words that also quietly show they are descendants of the word for cord or thread. Including:
Herir (Spanish for, “to round”; most commonly heard in the form, “herido”, a wound) is a surprising cousin of… interfere. How so?
Interfere comes to us from the French entre- (“between”) and ferir (“to hit”). Interfering with something is really just hitting it right in the middle of it, breaking it up! Ferir comes from the Latin, for the same, Ferire.
Curiously, Ferire evolved into Spanish Herir — the Initial “F” turning into a “H”. It turns out, this is a common pattern as Latin evolved into Spanish — but in no other language! Just look at Filial and Hijo, or File and Hilo, or Fig and Higo.
Thus, the h‑r of herir maps to the (int)-f‑r of interfere.
Fervor is really just an intense passion heating up. Thus we shouldn’t be surprised that it comes from the Latin root fervere (“to boil”), from which we get the Spanish for the same (“to boil”), hervir.
The seemingly unrelated words are connected through the common transformation of Latin words beginning with an f- into an h- in Spanish, such as fig and higo, and fable and hablar.
Thus, the f‑r-v of fervor maps to the h‑r-v of hervir.