In the evolution of Latin to Spanish, nouns ending -us generally evolved into -o, e.g. manus > mano

However this seems to have been avoided in a few words:

  • tribus > tribu
  • spiritus > espíritu
  • impetus > ímpetu

Why did these forms evolve, instead of the expected *espírito, *ímpeto, *tribo?

  • 1
    CORDE shows some 300 hits for "espirito", mostly in the 13th century (and some 24 for "espírito").
    – jacobo
    Commented Jan 26, 2019 at 23:42
  • 2
    It's interesting. In older Spanish there were a few other words occasionally that pop up with a U. The one that I can think of off the top of my head is Jesú (nowadays Jesús), and that should have gone to Jeso. So there are others, but they also maintained their -s Commented Jan 26, 2019 at 23:56
  • 1
    That's very interesting, never thought about that. My guess: usual sentences involved a word starting with "s" after such words. For example, "spiritus sanctus" → "spiritu |ssanctus". Does this make some sense? i have no idea, but it'd be interesting if someone could tell us.
    – FGSUZ
    Commented Jan 27, 2019 at 14:40

2 Answers 2


The short answer is because these words are cultismos or learned words.

According to Corominas, espíritu was taken directly from Latin in the 13th century:

DERIV. Espíritu, 1220-50, tom. del lat. spirĭtus, -us, íd.,

therefore it is a cultismo or learned word, and not a palabra patrimonial or natural word. It is a similar story for tribu and ímpetu:

TRIBU, 1490 (y ya alguna vez en el S. XIII). Tom. del lat. tribus...

ÍMPETU 'empuje', med. S. XV. Tom. del lat. ĭmpĕtus, -us...

For these cultismos, taken directly from Latin or Greek, the rules of natural language evolution do not apply, because there has not been continuous use from Latin to romance. Sometimes some of the basic rules apply to these words, like in the case of spiritus, where it loses the final -s, sometimes none. And sometimes these words change in their subsequent history as the language continues evolving.

There are some interesting examples in which two different words have the same origin, one being the natural evolution directly from Latin, the other being a later acquisition or cultismo. For instance:

  • operam > obra (patrominal) or ópera (cultismo)
  • laborare > labrar (patrominal) or laboral (cultismo)

A good introductory reading for these subjects is this article (in Spanish).


As you said, the regular development seems like it would have been -o, as in mano.

I just wanted to mention that in other respects as well, none of these words looks like a completely natural development from the Latin form. They don't show characteristic sound changes like short ĭ > e, syncope of unstressed vowels, and lenition of intervocalic singleton consonants. I think Latin trĭbus, spīrĭtus, impĕtus, if they had undergone all the usual Latin-to-Spanish sound changes, should have turned into something like *trevo, *espirdo, *ento. I'm not 100% sure on these forms, but I'm sure that neither tribu, espíritu, ímpetu, nor *tribo, *espírito, *ímpeto are expected vulgar forms.

So influence from Latin seems like a strong candidate.

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