sesquitertia

noun2

1. •
   (no longer used) A ratio of 4 to 3.

   • For, what proportion, 100 hath to 75: the same hath 17 1/7 to 12 6/7: Which is Sesquitertia: that is, as 4, to 3. which make 7. — 1570
2. •
   (no longer used) A perfect fourth, an interval having the ratio of 1 to 1⅓, or 3 to 4.