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.
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 hallar (“to find”) comes from the Latin afflare (“to blow.”) From that same Latin root we get various f-l words involving blowing, including:
All of these share the f-l root. But how did this turn into the Spanish hallar? Well, first remember that the initial F- sound tended to disappear when Latin turned into Spanish; see, fig and higo or fable and hablar. Secondly, note that finding something is just blowing on it, uncovering what was below the dust you blew away!
Hervir (Spanish for, “to boil”) comes from the Latin fervere (“to be hot, burn, boil”).
The best part: from this same root, we also get the English… fever!
This is thus another example of the pattern where Spanish lost the initial F and replaced it with the (unspoken) “H”: Hoja-Foliage, Huir-Fugitive, etc.