Suspect and the Spanish equivalent, sospechoso, are easy to identify and obviously the same word, both from the same Latin root, suspectus.
That’s not the interesting part. Rather, as Latin evolved into Spanish, the Latin sound ‑ct- turned into the Spanish ‑ch- sound. Think lactose/leche or octagon/ocho.
And suspect falls exactly into this pattern: the English s‑s-p-ct maps exactly to the Spanish s‑s-p-ch.
The law and the good, in European languages, are associated with straight lines; the bad with the crooked. Think about the word crooked itself, literally! Or about right/rectangle, or the Greek ortho- for straight, hence, orthodox as well as orthodontics.
This is why it makes sense that Derecho — Spanish for straight and also for law — comes from the same Latin root that gives us direct.
The “ct” in the original direct turned into a “ch” in Spanish, in the usual pattern of “ct” turning into “ch” as Latin grew into Spanish.
The Spanish for “night”, noche, is related (via the common Latin ancestor) nocturnal.
Here’s the interesting part: the Latin sound “ct” consistently changed to the “ch” sound in Spanish. Think “lactose” and “leche”, or “octagon” and “ocho”. And this is another example of that pattern: the “ct” in “nocturnal” is the same as the “ch” in “noche”!
Ah, one of our all-time favorite patterns and examples: leche, the common Spanish word meaning, “milk.”
Leche is a first cousin of the English lactose via a very interesting pattern: the ‑ct- to ‑ch- pattern.
Both come from the same Latin root, lactatio (literally, “suckling.”) The ‑ct- in that root remained unchanged as it entered English (because it entered via the sophisticated French) but that sound almost always turned into a ‑ch- sound as Latin evolved into Spanish. Thus the l‑ct maps to the l‑ch almost exactly.
Many other awesome words follow the same pattern: think octagon/ocho, for example. Some more coming up soon (or see the pattern page linked below).
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.