The Irish Examiner has an interesting article on Fenit with many historic facts to check out, including the old names for Fenit.
Logainm records many placenames for the island, including Feynan from 1472, Ó Fhiannaid from 1560, and Ffinittbeg from 1641. The current spelling appears to date from 1756 as recorded in Charles Smith’s The Ancient and Present State of the County of Kerry. A later version again gives it as Fíanaid, which translates as a wilderness.
Read the full article here: https://www.irishexaminer.com/property/homeandoutdoors/arid-40318664.html