Learn English – Why is it spelled “curiosity” instead of “curiousity?”

derivational-morphologyetymologyo-ouorthography

I have been spelling the word "curiosity" with a u, "curiousity," my whole life, and only today was Chrome's spellcheck bold enough to highlight my lifelong error. I have two questions:

  1. The root word is curious. How or why has the quality of being curious come to be spelled without its u? Or is it the word curious that is unique, and both words were derived from a word with no u, like curio?
  2. Since I have spelled the word this way my whole life and none of my English teachers/professors ever crossed out this "misspelling," is it not technically incorrect, just discouraged? Or perhaps it is archaic, which is why I could only find it defined in a legal dictionary with a capital "C:" Curiousity, not curiousity.

Best Answer

Interesting question! Here's what the OED has to say about -ious:

a compound suffix, consisting of the suffix -ous, added to an i which is part of another suffix, repr. Latin -iōsus, French -ieux, with sense ‘characterized by, full of’. ... by false analogy in cūriōsus curious (from cūra): see -ous suffix.

and, re: -ous:

Nouns of quality from adjectives in -ous (however derived), are regularly formed in -ousness , ... a considerable number of those from Latin -ōsus have forms in -osity , as curiosity ... see -osity suffix.

and, re: -osity:

The direct reflex of Latin -ōsitāt- in Old French was -ouseté , which is found in Middle English as -ouste , forming nouns from adjectives in -ous suffix... . Loanwords of this period having the latter termination and remaining in use were subsequently re-formed with -osity (e.g. contrariosity n., curiosity n.: compare also religiousty n., voluptuousty n. with religiosity n., voluptuosity n. (all first attested in late Middle English), and hidousty n. with the much later formation hideosity n.). ...

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