use it instead of these words: happiness, joy, contentment, pleasure.
variations: felicitous (use instead of happy), felicitate, felicitation (use plural instead of congratulations)
I felicitate you! He offered his felicitations. The felicities of summertime. There is no greater felicity than chocolate cake.
It's felicity. (Not just an American Girl, people!)
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Update:
gchat status 9/17/2009
"leads a felicitous life"