authentical

As an adjective authentical

is (archaic) authentic.

As an adverb really is

(lb) actually; in fact; in reality.

As an interjection really is

indicating surprise at, or requesting confirmation of, some new information; to express skepticism.

As adjectives the difference between authentical and genuine

is that authentical is (archaic) authentic while genuine is belonging to, or proceeding from the original stock; native; hence, not counterfeit, spurious, false, or adulterated; authentic; real; natural; true; pure.

As a noun taxonomy

is the science or the technique used to make a classification.

As an adjective authentical is

(archaic) authentic.