eirs vs his

eirs

pron
  • That which belongs to em, possessive case of gender-neutral ey, equivalent to the singular theirs and coordinate with his and hers. 

his

pron
  • That which belongs to him; the possessive case of he, used without a following noun. 

det
  • Belonging to him. 

How often have the words eirs and his occurred in a corpus of books? (source: Google Ngram Viewer )