The English foot comes from the Indo-European root *ped. Think pedal.
Interestingly, the “p” sound consistently transformed into an “f” in the Germanic languages — but remained a “p” in the Latinate languages.
This is why, foot is equivalent to pie.
Other examples of this pattern include father and padre, and the English far is from the same root as the Latin per.
The Spanish pudrir, “to rot,” has a surprising connection to the English, foul, a word meaning the same but sadly very underused these days — although still when quoting Macbeth: fair is foul and foul is fair!
Both come from the same Indo-European root *pu, meaning, “to rot.”
But the English one sounds so different because, in the Germanic branch of Indo-European, the p- sound turned into the f- sound. But now in the Latin branch.
Thus the initial f+vowel of foul maps to the initial f+vowel of pudrir.
From the same root are more fun words including defile, putrid, and pus. What wonderful imagery!
The Spanish pegar (“to paste”) comes from the Latin pix, meaning “tar.” That makes sense: “paste” looks like just a more diluated “tar.”
But pix itself comes from the Proto-Indo-European root pei(e), which meant, fat — think of animal fat, for example. It makes sense that this word evolved into a word meaning “tar”: that’s a bit what animal fat looks like.
From this same root pei(e), we get a few notable English words:
The Spanish for “foam”, espuma, comes from the Latin for the same: spuma. And this Latin comes from the Proto-Indo-European root *(s)poi-moi from which we also get the English… foam.
How so? Because the PIE root p- very consistently became an f- as it evolved into German then English, but this transformation never happened when it became Latin and then Spanish. Note words like foot/pie and father/padre.
Thus the f‑m of foam maps to the (s)-p‑m of espuma very clearly!
It is both surprising and funny that in Spanish, a Flea Market is translated to be, literally, exactly the same: Mercado de Pulgas.
But it is even more surprising (although probably less funny) that flea and its Spanish translation, pulga, are close cousins — despite the different sounds.
Both derive from the Indo-European *plou. To understand this transformation, we should remember that the Indo-European p- sounds stayed the same in Latin (and thus Spanish) but became an f- sound in German (and thus English).
Therefore, the f‑l of flea maps exactly to the p‑l of pulga!