Old English feortan, ultimately from PIE *perd- (source also of Old High German ferzan, Old Norse freta, Danish fjerte, Sanskrit pard, Greek perdein, Lithuanian perdžiu, persti, Russian perdet), of imitative origin. Related: Farted; farting. As a noun, from late 14c.
Clatterer or clatterfart, which wyl disclose anye light secreate. [Richard Huloet, "Abecedarium Anglo-Latinum," 1552]