An archaic or rare term, possibly referring to someone who makes, wears, or works with belts in some capacity.
From 'belt' plus the agent suffix '-er,' a standard way in English to form occupational or active nouns. This term appears to be largely obsolete.
Beltir would be to belts what a miller is to mills—someone professionally involved with them. It's another example of how English once had a word for nearly every job imaginable, but most have vanished!
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