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!
The relation between “five” in Spanish (cinco) and English is one of the more surprising relationships: they are indeed direct second cousins!
Both come from the same Proto-Indo-European root, *penkwe, meaning the same, five. (The greek for five also comes from the same: think about pentagon, for example).
The interesting part is this: the p- sound in Proto-Indo-European evolved into the Germanic and then English f- sound. Think about father and padre, for example or foot and pie. Five and cinco follow this pattern too, but in a more subtle way.
The Proto-Indo-European for the same, *penkwe, evolved into the Latin word for “five”: quinque. The qu- was pronounced in a hard way like a k- and then, as Latin evolved into Spanish, the k- was softened into the soft c- in cinco. So p- to k- to c-. You can see it through the similar sounds.
Indeed, the pattern is most obvious in the repetition of the sounds in both works cin-co as the c/k sound twice, at the start of each syllable. And the fi-ve as the f- sound (and its closely related, usually identical and often interchangeable sound of v-) at the start of each of its syllables as well.
Father is one of the most basic words in every language and a traceable pattern throughout the Indo-European languages.
The original PIE sound “p-” changed in all the Germanic languages to “f-“. This is referred to as “Grimm’s Law”, from the fairy-tale fabulist who first noted this pattern.
In the Latin languages such as Spanish, the original “p-” sound was preserved. Thus, the Spanish padre’s p-d-r root maps to the English father’s f-th-r root.
Pluma, Spanish for “feather”, sounds nothing like the English feather.
But it is a cousin to the English fleece.
Both come from the same Indo-European root *pleus-, which meant “feather” or to “pluck.”
But they sound so different! That is because the Indo-European p- sound stayed the same into Latin then Spanish, but changed into a f- in the Germanic branch (including English).
Thus the p-l of pluma maps to the f-l of fleece.