If he is fuming, he is smoking — literally. And it is, subtly, the same word in Spanish.
“To fume” comes from the Latin root fumus (“smoke”) from which we also get the common Spanish word for “smoke”, humo. But they don’t sound alike, so how are they related?
The Spanish humo is a great example of the pattern of the Initial F turning into an H in Spanish, alone among the languages of the world. Many Latin words that began with an F, and come to us in English through the Latinate F form, became the equivalent word but with an H- in Spanish. Take hermano and filial, for example. Or fact and hecho.
Other English words from the same root fumus include fumigation (ahhhh!) and the less common fetid. Fetid is a dirty, Shakespearean word, after all.
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.
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.
From the same Latin root fusus, we also get the English… fuse. Why? Well, look at the shape: an old-school spindle looks like a big fuse!
Thus, we can see the f-s of fuse map clearly to the h-s of huso.
Hombre, Spanish for “man”, comes from the Latin for the same, hominid. From the same root, we get the English hominid and the classic ad hominem attack.
Here’s the interesting part: the m-n sound in Latin consistently changed into the -mbr- sound in Spanish. Thus, we have parallels like nombre and nominal. And hombre maps exactly to this pattern with both ad hominem and hominid.