IPA: /ˌmæθəˈmætɪʃən/
KK: /mæθəˈmætɪʃən/
A person who is very good at or has a lot of knowledge about mathematics.
The mathematician solved complex equations that others found difficult.
Mathematician → It is formed from "mathematics" (from Greek "mathematikos", meaning skilled in learning) and "-ian" (meaning a person who). A mathematician is a person skilled in the study of mathematics.
Think of someone who is 'skilled in learning' ('mathematikos') about numbers and shapes — that's what a mathematician does.