If you read something in the original, you read it in the language in which it was first written: As part of his studies, he read Homer in the original.

Originalism is a theory of the interpretation of legal texts, including the text of the Constitution. Originalists believe that the constitutional text ought to be given the original public meaning that it would have had at the time that it became law.

: of, relating to, or constituting an origin or beginning : initial the original part of the house 2 a : not secondary, derivative, or imitative an original composition b : being the first instance or source from which a copy, reproduction, or translation is or can be made