Is it ensure, insure, or assure?
late 14c., from Latin Faunus, a word of unknown origin. A god of the countryside, worshipped especially by farmers and shepherds, equivalent of Greek Pan. Formerly men with goat horns and tails, later with goat legs, which caused them to be assimilated to satyrs, but they have diverged again lately.
The faun is now regarded rather as the type of unsophisticated & the satyr of unpurified man; the first is man still in intimate communion with Nature, the second is man still swayed by bestial passions. [Fowler]The plural is fauni.