^I'm pretty sure some words on the chorus doesn't exist at all, considering Timmy even said we couldn't find all of them on a dictionary...
We do have spanish native speakers, italian native speakers and french native speakers over here, and none recognized any word on the whole song besides the ending chorus with the "good byes"... So, it doesn't really matter on what language the word was intented to be, considering considering the chants are in neither language...
And also, this word DOES exist in English... I find it easier to believe that she pick it on a English dictionary...
Brillante
Bril*lan"te\, adv. [It. See Brilliant, a.] (Mus.) In a gay, showy, and sparkling style.
http://dictionary.reference.com/browse/brillante