"Strepitant" (and the related "strepitous") are adjectives meaning boisterous or very noisy. Both come from the Latin "strepitantem," present participle of "strepitare," from "strepere" (to make noise). The Oxford English Dictionary records strepitant being used in 1842 and 1861, with "strepitantly" as late as 1913, but the vast majority of the Google results in a search for the word turn up Latin documents, so it's certainly an obscure term in English. (Though a 1915 letter at http://www.ku.edu/~libsite/wwi-www/Chapin/Chapin04.htm seems to use "strepitant" without having yet made it into the OED.) Perhaps the most common English usage is in quoting this poem:
"Three makes rejoinder, expansive, explosive;
Four overbears them all, strident and strepitant"

Robert Browning, "Master Hugues of Saxe-Gotha,' Dramatic Lyrics, 1842.