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!
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.