FAT'UOUS, adjective [Latin fatuus.] 1. Feeble in mind; weak; silly; stupid; foolish. 2. Impotent; without force or fire; illusory; alluding to the ignis fatuus. Thence fatuous fires and meteors take their birth.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI