seventy-oneth

adj, noun — 2 senses

adj

/ˌsɛvənti ˈwʌnθ/

Etymology From seventy-one + -th (ordinal suffix).

Nonstandard seventy-first

noun

Etymology From seventy-one + -th (ordinal suffix).

Nonstandard seventy-first (a fractional part of seventy-one)

he found ... that the circumference was three times the diameter plus a quantity which was less than a seventh but more than ten seventy-oneᵗʰˢ.1892, Frederic Harrison, “Archimedes”, in The new calendar of great men, page 124:

Entry derived from the Wiktionary, under licence CC BY-SA 4.0 — list of authors.