膨大
ぼうだい · boudai · JLPT N2 · na-adj
enormous
🐘 膨 = swell, 大 = big: something that swells up big is enormous
膨 means swell or bulge, and 大 means big. Something that keeps swelling becomes enormous or extensive. The same 膨 appears in 膨張 (expansion).
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.