the fundamental assumptions from which something is begun or developed or calculated or explained
"the whole argument rested on a basis of conjecture"
A physical base or foundation.
"The old lighthouse stood on a rocky basis that had weathered centuries of storms without cracking."
In plain English: A basis is the main idea or foundation that something is built on.
"The success of their business is based on good customer service."
Usage: Use "basis" to mean the underlying principle, fact, or foundation upon which something is built or operates. It refers to the abstract support for an argument, system, or situation rather than a physical object.
The word "basis" comes from the Latin basis, which was borrowed from Ancient Greek básis meaning "a step" or "a foundation." It entered English as a doublet of the word "base," sharing the same ultimate origin in the Proto-Indo-European root gʷem-.