I have the impression that the ending -m appears on neuter nouns (in the nominative/accusative form) only in the second declension, but I don't know whether there are any exceptions. Is there any example of a neuter noun ending in -m that belongs to a declension other than the second?
I know that Latin nouns sometimes had multiple declension patterns or multiple genders. For the purpose of this question, I'd accept a word that belongs to multiple declensions/genders, as long as it's clear that the neuter nominative/accusative form ending in -m isn't just part of a complete regular second-declension paradigm.
If no such words exist, I would be interested in knowing whether there is any etymological explanation.