[I]f we connect the fact that Fatuus is said to be an alternative name for Faunus, and that he predicted the future, and that this god is attested on an Etruscan mirror as Fatuvs in a clear oracular function (Weiss 2007b), we may venture a derivation from forfor 'to say' (Untermann 2000). The name of the god would then have come to be used pejoratively as 'silly'. [de Vaan]Related: Fatuously; fatuousness.
来自拉丁语fatuus, 愚蠢的，无味的。可能进一步来自PIE*bhat, 击，打，词源同beat, batten. 委婉语，脑子出问题的。