What is a binnial?

Answer 1

I don't think there is such a word as binnial.

Maybe you meant biennial which means occuring every two years or lasting for two years.

Answer 2

A biennial is a plant that completes its life cycle in two years, typically flowering and producing seed in the second year. It differs from annuals, which complete their life cycle in one year, and perennials, which live for more than two years.