paralogism

noun

pa·​ral·​o·​gism pə-ˈra-lə-ˌji-zəm 

: a fallacious argument

Word History

Etymology

Middle French paralogisme, from Late Latin paralogismus, from Greek paralogismos, from paralogos unreasonable, from para- + logos speech, reason — more at legend

First Known Use

1565, in the meaning defined above