1871: coined by Lewis Carroll in Through the Looking Glass, apparently to suggest fair and joyous.
“Oh what a frabjous day we had today!”
Pompous or extravagant in language, style, or manner, especially in a way that is intended to impress.
Late 16th century: from Latin grandiloquus, literally ‘grand-speaking’, from grandis ‘grand’ + loqui ‘speak’. The ending was altered in English by association with eloquent.