The Collaborative International Dictionary of English v.0.48:

Joyous \Joy"ous\, a. [OE. joyous, joious, joios, F. joyeux.See
   Joy.]
   Glad; gay; merry; joyful; also, affording or inspiring joy;
   with of before the word or words expressing the cause of joy.
   [1913 Webster]

         Is this your joyous city?                --Is. xxiii.
                                                  7.
   [1913 Webster]

         They all as glad as birds of joyous prime. --Spenser.
   [1913 Webster]

         And joyous of our conquest early won.    --Dryden.

   Syn: Merry; lively; blithe; gleeful; gay; glad; mirthful;
        sportive; festive; joyful; happy; blissful; charming;
        delightful. -- Joy"ous*ly, adv. -- Joy"ous*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

joyousness
    n 1: the emotion of great happiness [syn: joy, joyousness,
         joyfulness] [ant: sorrow]