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.
The Spanish celoso and the English for the same, jealousy, come from the same Greek root: zelos.
But how did this happen? They should so different!
The answer is that the Latin (and Greek) words with a -ch- sound and variations (like -sh-, the soft -j-, -z-, etc) usually turned into the hard, guttural, throat-cleaing -j- sound in Spanish. Think about sherry and jerez, for example, or quash and quejar, or soap and jabón.
Thus, the c-l-s of celoso maps to the j-l-s of jealous.
Curiously, the ancient Greek form — zelos — meant jealousy, but in the more positive sense of enthusiasm and friendly rivalry. In a word: zeal — which also comes from the same root!
Hombre, Spanish for “man”, comes from the Latin for the same, hominid. From the same root, we get the English hominid and the classic ad hominem attack.
Here’s the interesting part: the m-n sound in Latin consistently changed into the -mbr- sound in Spanish. Thus, we have parallels like nombre and nominal. And hombre maps exactly to this pattern with both ad hominem and hominid.
Daño, Spanish for “damage”, comes from the Latin for the same: damnum. From the same root we get both the English condemn and damn. But what happened to that missing ‘m’?
Interestingly, the Latin m-n sound tended to turn into a ñ sound in Spanish. This explains how autumn became otoño, for example.
We can still see this pattern preserved in the perfect mapping of d-ñ in daño to the d-mn of damn, and the same with condemn.
From the same root we also get the English indemnity, as well as damage itself, although the final -n was lost because damage entered English via French.
We can see the parallel but between daño, condemn, damage, and damnum — but how did it come to mean the formerly-vulgar, damn? Think of damn in the old sense of, sentencing someone for a crime they did: you are condemned to hell. A whole slew of English insults come from this same concept, including the word hell itself!
The Spanish caja (“box”) comes from the Latin capsa for the same.
This gives us a surprising connection to some English words that, on the surface, sound very different than caja:
The Latin turned into the Spanish through an interesting pattern: the -sh- sound in Latin consistently turned into the -j- sound in Spanish (at first retaining the original pronunciation, but then under the influence of Arabic, grew to the throat-clearing sound). With caja, we have a slight variation of the pattern, where the -ps- sound turned into the -j- sound. Thus, the c-ps maps exactly to c-j.