An easy way to remember the Spanish decir (to say) is through the word predict.
Predict is, literally, pre – decir — to say beforehand. Pre means “before” and the dict- maps almost exactly to the Spanish decir.
How come the decir has an extra -t in it to be predict? Because the Latin predecire took the grammatical form of predicatus and this form grew into English (via the French influence). A prediction in Spanish, after all, is predicho!
Thus, it is a cousin of many English words such as diction and dictionary.
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 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.
The Spanish hechizo (“spell”; nothing to do with the letters in words, but what a witch casts on you!) comes from the Latin facticius (“made by art”; “artificial” — indeed, that which is artificial is just something not occurring naturally but instead made by art!).
But how did artificial change to mean “spell”? Think about it this way: casting a spell goes against nature — it’s what the wicked, crazy and profoundly unnatural woman does! Think of the three weird sisters in Macbeth, and how they unnaturally stir up all the elements!
From hechizo (more specifically, from it’s Portuguese twin cognate, feitiço), we get the English fetish. How? Well, you have a fetish when the recipient casts a spell on you to become obsessed with the object of your fetish, right? Enough said!
That root facticius turned into hechizo by changing via two common patterns: the initial F in Latin tended to turn into an H as Latin turned into Spanish (compare fig and higo, or fume and humo!) and the -ct- tended to change to a -ch- (compare noche and noctural; or ocho and octagon). Thus the h-ch of hechizo maps to the f-sh of fetish.
Luchar, Spanish for “to fight”, doesn’t sound like its cousin reluctant – although of course everyone is reluctant to fight. But the relationship is closer than it seems.
Reluctant comes from the Latin roots re- (“against”) and luctari (“to fight”). Reluctance is to fight against what should be done — literally.
From luctari, we also get the Spanish for exactly the same, “to fight.”
But they don’t sound similar. How did luchar evolve?
Interestingly, in most Latin words that had a -ct- sound, this -ct- sound evolved into -ch- as Latin evolved into Spanish. Think about night/noche and eight/octagon. The same pattern explains luctari turning into luchar.
We see this relationship clearly with the l-ct to l-ch mapping between the two.