How does the word assurance become a noun?

The word "assurance" is already a noun. It has been a noun for centuries.

The word "assurance" comes from the Old French word "assurance," which in turn comes from the Latin word "assurare," meaning "to make secure."

Assurance as a noun has several meanings, including:

* Confidence or certainty: "He spoke with an assurance that was both charming and unnerving."

* A promise or guarantee: "The company offered an assurance of a full refund if the product didn't meet expectations."

* Insurance: "Life assurance is a vital part of financial planning."

It's possible you're thinking of a different word or perhaps mistaking the use of "assurance" as an adjective (e.g., "an assured victory").