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.
We’ve previously discussed cuerno (Spanish for horn) and its related Spanish words–and here’s another: cornucopia, which literally means… the “horn of plenty.” We see the h‑r-n map to the c‑r-n again here!
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 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.
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: