Autodidact
Etymology
From Greek "autodidaktos," self-taught (autos, self + didaktos, taught). The same "didaktos" root gives "didactic."
noun · /aw-toh-DY-dakt/
A person who has taught themselves a subject without formal instruction.
What it names
A mode of learning — self-directed, teacherless — rather than a level of talent.
Example
A high-school dropout and lifelong autodidact, she learned three languages and read her way through the entire philosophy shelf.
Related idea
Often overlapping with the polymath but defined by method, not range; the autodidact learns straight from the didactic text, without the teacher.