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.
The Spanish correr, “to run” seems completely unrelated to the English horse. Looks can be deceiving.
Correr comes from the Latin for the same, currere. Currere, in turn, comes from the Proto-Indo-European root *kurs, which also means, “to run” — just like horse does! Both have the same common ancestor.
The weird thing is: how did the PIE *kurs turn into horse, they sound so different.
The explanation is that, in the Germanic languages like English, the k- sound turned into the h- sound. But in Spanish, the original k- sound remained, although usually written with a c-.
This explains many parallel words that have c- and h- sounds that map to each other between Spanish and English, like heart/corazon and head/cabeza.
The Spanish for “horn”, cuerno (and its variations, like the ever-present cornudo), and the English horn are both originally the same word in the ancient languages.
One of the most interesting sound shifts is the Indo-European “k-” sound remained the same into Latin and then Spanish (the Latin cornu for the same) but became an almost-silent “h-” in the Germanic languages.
Thus the c‑r-n in Spanish parallels exactly the h‑r-n in English.
There are lots of awesome and subtle examples of this pattern, such as Corazon/Heart.
Today is time for what is perhaps my all-time favorite example of how sound patterns change over time. Here we go, no more delays:
The Proto-Indo-European sound k- changed into the h- sound into German (then English) — but it remained the k- sound (often spelled with c-) into Latin then Spanish. Thus we get many great parallels we’ve discussed before, such as head/cabeza. Another example of the same pattern:
The English hemp, for everyone’s favorite weed to smoke. The Spanish for the same, which we also say in English, is cannabis.
Now look closely: if we remember that the h- in the Germanic/English words maps to the c- in Latinate/Spanish words, then it becomes very clear that the h‑m-p of hemp maps the c‑n-b of cannabis. The m/n and p/b cross and change very easily between each other, so those sound changes are much more obvious.
Who would’ve thunk!
The Spanish for “son”, hijo, doesn’t sound like anything in English. But it is a close cousin of the English synonym for brotherliness: filial.
Both come from the Latin for “son,” filius. The transformation to Spanish came about through two interesting patterns: the initial f- in Latin usually turned into an h- in Spanish (such as, hacer and fact, or hablar and fable). The other pattern is less common: the ‑li- sound turned into a ‑j- sound — it’s just a less common sound! Thus the f‑li maps to h‑j almost exactly.
From the Latin filius, we get a few other English words, including: affiliate: an affiliate is, in a way, a child you rear!
From the same root we also get the English fetus, fecund and even feminine. These come, via the Latin filius, from the Proto-Indo-European root *dʰeh₁y-li-os, meaning, “sucker” — in the literal sense of, “one who sucks.” Children, indeed, are defined by their sucking their mothers; so your hijo is literally, “the one who sucks.” And, some might argue, even affiliates themselves usually do suck!