Carl Abel was a German linguist known for his research on Indo-European and Hamito-Semitic lexicology, which was published in his Einleitung in ein Aegyptischsemitisch indoeuropeanisches Wurzelwörterbuch (1886).

It was his theory of the "opposite meanings of primitive words" that interested Freud when, after alluding to the idea in the Interpretation of Dreams (1900a), he wrote an article on the subject ten years later, entitled "The Antithetical Meaning of Primal Words" (1910e). The theory appeared in Abel's article "Über den Gegensinn der Urworte," which appeared in Sprachwissenschaftliche Abhandungen, published in Leipzig in 1885.

Basing his thesis on the fact that a Latin word such as sacer signified both "sacred" and "taboo," Abel proposed a theory of the way vocabulary evolves in languages. For Abel, a word in its primitive state can have opposite meanings, which are gradually...