Llenar comes from the Latin plere (“to fill”), as we’ve previously discussed. But here’s another English word that comes from the same Latin root: expletive, yes, that euphemism for vulgar words!
Expletive literally means to “fill” with the expansive ex- prefix which, taken together, mean, “to fill out your words.” An expletive is literally filling conversation with words when you don’t know what else to say!
Llenar — Spanish meaning “to fill” — comes from the Latin plenus, meaning “full”.
This, therefore, connects it to the English for the same, from the same root: Plenty. Not to mention, the less common English word plenary.
These words sound so different yet they’re so similar. Here’s how: Latin words that began with pl- usually turned into ll- when Latin evolved into Spanish. But as these words moved into English via French, they remained unchanged.
This explains not just llenar/plenty but explains a bunch of other words, including llama/flame.
The Spanish lluvia (for “rain”) comes Latin pluvia for the same — a change that may not be obvious because the -pl- of Latin sometimes became a -ll- in Spanish.
From the same root, we get the sophisticated English word pluvial which means… lots of rain!
The ll‑v of lluvia clearly maps to the p‑l of pluvial.