How does the word "cardinal" relate to "cardinal numbers" [duplicate]

Cardinals are quite simply the primary, most ‘basic’ form of numerals.

Different languages have different categories of numbers (English has cardinals, numerals, and a few repetitionals or multiplicatives [once, twice]; Latin has these as well as distributives; Irish has animatives; etc.), but if a given language has numerals at all, it will almost certainly have at least cardinals.

The other types of numbers are given names for what they indicate apart from numeric values: ordinals indicate an ordering, etc.

Cardinals, being the primary type, indicates just the numeric value and nothing else.