The Spanish mancha (“spot” or “stain”) comes from the Latin for the same, macula.
From the Latin macula, we get the English… immaculate — which literally means (knowing the negation prefix of im-) “without a stain.” So the immaculate conception truly was perfect!
How this sound changed was interesting: often Latin words with a ct- or cl- or other hard letters after a c- sound turn into a suave ch in Spanish. For a distant example, see duct and ducha, or nocturnal and noche. (The ct- is much more common than the cl‑, but they’re cousins!) Thus, we can see the m‑ch of mancha mapping to the (im-)m‑cl of immaculate.
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:
Apostar, Spanish for “to bet”, sounds nothing like bet or any related English word.
But it turns out to be a close cousin of Posit and Position: Betting is indeed just an extreme form of putting forth a position or positing something — literally putting your money where your mouth is.
All come from the same Latin, positionem, which come from the Latin root verb ponere (“to put”) from which we also get the Spanish for the same, poner.
Both the Spanish reírse (“to laugh”) and the English ridiculous come from the same Latin root: ridere (also “to laugh”).
Thus, the r‑vowel-d-vowel of ridiculous maps to the r‑vowel-disappeared-vowel of reírse. Note that the middle ‑d- disappeared in the Spanish version, probably as the word was shortened since the Spaniards spent so much time laughing, it became natural to say it shorter and quicker!
Trapo is the common Spanish word for “cloth” or, more commonly, “rag”.
It sounds nothing like the similar words in English, except… it turns out to be a close cousin of drape & drapery.
All come from the same old Irish word, drapih, meaning, “garment.”
We can see the parallel in the t‑r-p and d‑r-p mapping. Both are the same roots except for the t/d shift, which is a very common and not-noteworthy transition.
A drape, after all, is a form of a cloth.