ratiocinate
verb
ra·ti·o·ci·nate ˌra-tē-ˈō-sə-ˌnāt 
ˌra-shē-,
-ˈä-
ratiocinated; ratiocinating
intransitive verb
: reason
ratiocinator
ˌra-tē-ˈō-sə-ˌnā-tər
noun ˌra-shē-
-ˈä-
Word History
Etymology
Latin ratiocinatus, past participle of ratiocinari to reckon, from ratio + -cinari (as in vaticinari to prophesy) — more at vaticinate
First Known Use
1643, in the meaning defined above