IPA: /ləˈdʒɪʃən/
KK: /lɒˈdʒɪʃən/
A person who studies or practices logic, which is the science of reasoning and argumentation.
The logician presented a compelling argument during the debate.
Logician → It is formed from "logica" (from Greek "logikē", meaning reasoning or logic) and "-ian" (meaning a person who practices or is concerned with). A logician is a person who specializes in reasoning or logic.
Think of someone who practices 'reasoning' ('logica') — that's what a logician does.