PLAGIARIST

an act or instance of using or closely imitating the language and thoughts of another author without authorization and the representation of that author's work as one's own, as by not crediting the original author: It is said that he plagiarized Thoreau's plagiarism of a line written by Montaigne. Synonyms: appropriation, infringement, piracy, counterfeiting; theft, borrowing, cribbing, passing off.

a piece of writing or other work reflecting such unauthorized use or imitation: “These two manuscripts are clearly plagiarisms,” the editor said, tossing them angrily on the floor.