The husk and stray are counted as sub-variants of existing mobs as opposed to entirely new mobs, hence why you are unable to simply type /summon Stray or /summon Husk. There was supposed to be spawn eggs for them, but it seems they were removed either intentionally or by accident in the final release.
Axiomatic method, in logic, a procedure by which an entire system (e.g., a science) is generated in accordance with specified rules by logical deduction from certain basic propositions (axioms or postulates), which in turn are constructed from a few terms taken as primitive.
Definition of axiom. 1  1 : a statement accepted as true as the basis for argument or inference : postulate 1 one of the axioms of the theory of evolution. 2  2 : an established rule or principle or a self-evident truth cites the axiom âno one gives what he does not haveâ. 3  3 : a maxim widely accepted on its intrinsic merit the axioms of wisdom.