|Sources||Ben na Main: various pre OS texts
Ping mein, mēin / Ben a Main Ping i mēn, also mēĭn: Diack MS2276
ben mae-in (middle hill). A. M. Alexander, Some Name-Pronunciations, Cairngorm Journal 1946, 269
Ben Main: A. Watson informants
Sabhalan Beinn Mheadhon: Seton Gordon and Watson correspondence
The forms, without a lenitied specific, and without any evidence of an initial article suggest this name is something other than meadhan. A. Watson gives other forms, all with an –m- rather than –bh-.
The same texts which give Ben na Main also give Ben na buird which is Beinn Bùird, so possibly this is Beinn Meadhan, ‘mid-mountain’ with meadhan acting as a noun rather than an adjective.