大胆
だいたん · daitan · JLPT N1 · na-adj
bold
大 — pictograph of a person with arms outstretched
大 is a pictograph showing a person standing with arms and legs spread wide. The outstretched arms suggest 'big' or 'great', extending from the literal image of a large stance to abstract meanings like important or grand. It is one of the oldest characters, found on oracle bones.
胆 — flesh radical 月 (肉) + 旦 dàn (phonetic)
胆 is a phono-semantic compound. The 月 component here is the 'flesh/meat' radical (肉), marking it as a body part — the gallbladder. 旦 (dàn) gives the sound. By extension, since the gallbladder was traditionally linked to courage, 胆 also means 'guts' or 'bravery'.