An archaic or obsolete spelling of 'air' or possibly a variant of 'heir' in some medieval contexts.
Either from Old French 'air' (air, atmosphere) or potentially influenced by 'heir' (inheritor), the spelling 'eyr' represents inconsistent medieval orthography.
Medieval writers spelled 'air' so many ways ('air', 'eyr', 'aer', 'ayre') that you could almost identify someone's region just by how they wrote this single word!
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