Let D be a placeholder for any set.
Let N be the set of natural numbers.
Definition 1: Cardinality is the "size" of D (notated as |D|) iff it is related to the members of N, where 0 is a member of N.
"related to" means that Cardinality is not necessarily some particular N member, yet it is at the domain of N, where N does not have the greater successor.
That didn't cut it as a definition that last time you posted it. Reposting it now doesn't improve on that.
The definition body itself is "grammatical" nonsense. You have presented "Cardinality is the 'size' of D" as a true/false proposition. So, in some cases cardinality is the "size" of D, and in other cases it is not. Great, I suppose, but what does cardinality actually mean?
As for "'related to' means that Cardinality is not necessarily some particular N member", you haven't described with any specificity what 'related to' means.
From your definitions, and only your definitions, with no extra hand-waving or undefined filler, how would one determine the cardinality of some set, S?
From your definitions, and only your definitions, with no extra hand-waving or undefined filler, how would one determine the cardinality of a set, {a,b,c,d}, to be 4 and not be 21?