In Latin (and daughter languages), there seems to be a correspondence between nouns of the third declension in -or/-us, -oris denoting a quality, and adjectives of the Ist class in -idus,a,um denoting something or someone possessing the corresponding quality (sometimes approximately, I guess out of semantic drift).

Here are the ones that I could find in Italian (some in Latin). I'm sure there are more, but these are already many enough to suggest a pattern:

  • CALOR, CALIDUS (Latin)


  • HUMOR (as in liquid), HUMIDUS (Latin)

  • AMOR (as in cohesion), AMIDUS (Latin)

  • timore, timido (Italian)

  • pavore, pavido

  • pallore, pallido

  • candore, candido

  • squallore, squallido

  • valore, valido

  • fetore, fetido

  • sapore, sapido

  • tumore, tumido

So, what is the pattern, and how did it originate? Is this appearing also in other IE languages?

  • Latin SE would be a good place for this question.
    – TKR
    Nov 18 '20 at 1:38
  • 1
    If -or stems from -ios after rhotacizm (as in maioris), and if -s is nominative (for nominalized adjectives), then you would have to compare -r (-s) and *-dus, eventually. If -d- can be understood the same as in cre-do, then calidus is approximately warm-ing, that which makes warm, whereas calor is simply warm. Yes? To be honest, I have no idea if that makes sense. Otherwise I would post it in a more complete form as an answer.
    – vectory
    Nov 18 '20 at 13:44

According to Wiktionary, -idus is "suffix forming adjectives", but most of the words in the Category:Latin words suffixed with -idus, are based on a verb.

-or is similarly "used to form a third-declension masculine abstract noun from a verb root or conceived root form"

So the relationship is that these are morphemes commonly used to form an adjective and an abstract noun respectively from a (usually verbal) root.


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