I. | ̷ ̷ ̷ ̷| ̷ ̷ adjective
1. : being number 81 in a countable series
the eighty-first day
— see number table
2. : being one of 81 equal parts into which something is divisible
an eighty-first share of the money
II. noun
1. : number 81 in a countable series
2. : the quotient of a unit divided by 81 : one of 81 equal parts of something
one eighty-first of the total