Their reasoning was dismissed as a circular argument: the Earth is flat because the map shows it to be, and the map is accurate because it's based on the Earth being flat.

circular 来自名词 circle（圆圈），加上形容词后缀 -ar 构成形容词，字面意思是"圆形的"，引申为"循环的、绕圈子的"。 circular argument 指"循环论证"，即用结论本身来证明结论的逻辑谬误，就像在原地绕圈一样没有实质进展。