Soap and the Spanish for the same, jabón, sound like they have nothing in common. But sounds can be deceiving.
Both come from the same root: the Latin sebum, meaning “grease”.
How can such different words be so related? Easy: the Latin s- sound and its variations (sh-, ch- and sy- for example) usually became, under the arabic influence, a j- sound in Spanish but remained more intact in English.
Thus, the s-p of soap maps almost exactly to the j-b of jabón. The “p” and “b” are often easily interchanged as well.
Less fun is also noting that, from the same Latin root, meaning “grease” we also get seborrhea (a medical condition of having too much grease on your skin).
Ajedrez (Spanish for “chess”) sounds nothing like the English chess, so they can’t be first cousins… right?
Wrong. The Spanish “j” sound — pronounced with an Arabic-ish throat-clearing sound — was originally pronounced with a “sh” or “ch” sound. The arabic influence changed the pronunciation to be closer to the arabic: see sherry/jerez, for example.
Ajedrez and Chess are another example of this same interesting pattern. Try to imagine the “j” in ajedrez with a ch- sound and you almost get chess.
Both, curiously, come from the same Sanskrit word for the game: chaturanga (so the English ch- is thus preserved closer to the original sound — English didn’t have the arabic influence that Spanish did). And these came to both languages via the Persian, chatrang. The traders and travelers, after all, are the ones who change languages.
The Latin sounds for “sh” — and similar variations, like “ch” and “ss” — became a “j” sound in Spanish.
Thus, the English sherry is near identical to the Spanish jerez!
These sh/j sounds were often spelt with a “x” in old Spanish; and sherry itself is named after the town it first came from, Xeres, which is near Cordova.
Chief, and the Spanish for the same, Jefe, both come from the same root: the French chef, which means the same.
But this is odd as they sound so different! How are they related?
It’s not obvious, but it’s easy once you understand the pattern: The Latin sound “sh” and very similar sounds (such as the “ch” and “sy”) almost always became a “j” in Spanish. Like syrup and jarabe. Not obvious!
Jeringa, Spanish for Syringe, sounds like it has nothing in common with its English counter-part. But they are literally the same word.
The Latin sh- sound often evolved into the j- sound in Spanish — originally retaining the sh- sound but eventually, under Arabic’s influence, transforming to the throat-clearing sound we know and love.
This explains how both jeringa and syringe derive from the same root: the Latin siringa, itself from the Greek syringa. The sy- sound is a variation of the sh- sound and therefore the sy-r-n-g of syringe maps to the j-r-n-g of jeringa.