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.
  • 11
    As far as English is concerned, the root of curiosity is curiosity. It was not formed from curious. The real question here is where the latter got its second u from. The French original did not have it. (Edit: and the answer to that, of course, is rather boring: by analogy with all the other -ous words. Dangerous, numerous, devious, perilous, dubious, serious, oblivious, murderous, hilarious, marvellous, what have you. It actually makes perfect sense for once.)
    – RegDwigнt
    Sep 18, 2014 at 21:08
  • 3
    @Reg: Surely there must be more to it than that. What about monstrosity, religiosity, generosity, etc.? Sep 18, 2014 at 21:26
  • 3
    Also: generous and generosity.
    – jxh
    Sep 18, 2014 at 22:02
  • 1
    And monstrous and monstrosity.
    – Barmar
    Sep 19, 2014 at 20:14
  • 1
    @FumbleFingers same as at Janus, you are not contradicting anything I just said. Always a u if there's no -ity, always none otherwise.
    – RegDwigнt
    Sep 19, 2014 at 21:28

2 Answers 2


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.). ...


The base (root) is "cure".

cur(e) + i + ous = curious

cur(e) + i + o(u)s + ity = curiosity

EXPLANATION --The "i" is explained above by szarka.
--The "e" is dropped as usual when adding the suffix that starts with a vowel. --The "u" is dropped in "curiosity" as part of another suffix spelling pattern (i.e., when adding the suffix "-ity" to a word ending with the suffix "-ous" drop the "u".) Another example of this pattern is "luminous"->"luminosity".

See: curious. (n.d.). Online Etymology Dictionary. Retrieved August 08, 2015, from Dictionary.com website: http://dictionary.reference.com/browse/curious

  • What is szarka that you're referring to here?
    – ngood97
    Sep 26, 2023 at 15:59

Not the answer you're looking for? Browse other questions tagged or ask your own question.