Thread:User talk:CodeCat/Could you check this over/reply (4)

In both cases I believe it was reanalysis. This may just be idle rambling from having looked at these too long, but it seems plausible to me.
 * For -mentum, there are examples like armentum, whose earlier form (armenta) is 1st declension. This would then have been reanalyzed as the neuter plural.
 * Similarly, I suspect the that -μᾰ was suppletive (*-mn̥, *-mn̥th₂) and the t-stem crept back into all the singular forms except the nominative singular.