The English for eager-to-fight, pugnacious, contains the ‑gn- pattern inside it: a give-away to the pattern that ‑gn- words in Latin turned the ‑gn- into a ‑ñ- in Spanish yet remained the same into English.
Therefore, pugnacious maps perfectly to puñal, the Spanish for… “dagger.” It makes sense that “dagger” and “eager to fight” come from the same root, after all. And that root, in this case, is the Latin pugnare, meaning, “to fight.”
The Latin words that began with “cl” changed, pretty consistently, to “ll” as Latin changed into Spanish.
Today’s example of this: the Latin word for “key” was clavis. This became the modern Spanish word for “key”, llave.
There are, however, a few interesting other descendants of clavis, and thus distant relatives of llave. They include:
Sueño (Spanish for “dream”) and insomnia come from the same root: the Latin somnus, meaning, “sleep.”
The evolution is easy to spot if we remember that the ‑mn- sound in Latin usually transformed into the ñ in Spanish. See damn and daño, for example. Or autumn and otoño as well.
Thus, the s‑mn of insomnia maps to the s‑ñ of, sueño.
Tamaño (Spanish for “size,” in the size of, “what is your pants size?”) comes from the Latin tam — magno, that is, “so — great” (“great” in the size of “big”). Tam is the Latin for “so” or “very” from which we get the Spanish tan.
To even measure is thus to imply that… you are big! So great! If you’re small, after all, you don’t even need to measure it!
Magno (Latin for “great” or “big”) gives us the English… magnificent. But, curiously, the -gn- turns into the ñ as Latin evolved into Spanish. Thus tan — magno became tamaño. We see this gn to ñ pattern in many words, such as cognate / cuñado.
The Spanish rehusar — literally, “refuse” — sounds odd to English ears: it’s the same word, but the ‑f- became an ‑h-. Huh?
This is explained via the pattern of Latin words that began with an f- tended to turn into an h- in Spanish and only in Spanish. See famine/hambre, and huir/fugitive for example.
Refuse and Rehusar follow the same pattern. Both come from the Latin refundere — from which we also get the English, refund. They are all ways of giving back.
This f‑to‑h pattern usually happens with the first letter of the word. But here it is the first letter of the second syllable — because the re- is of course the standard prefix so it didn’t effect the sound pattern change.