盛大
せいだい · seidai · JLPT N1 · na-adj
grand
盛 — 成 (chéng, phonetic) + 皿 (vessel)
A phono-semantic compound: 皿 (a dish or vessel) gives the meaning, while 成 supplies the sound. The original sense was grain heaped into a ritual vessel as an offering, hence 'to fill' or 'contain' (chéng). From 'full to the brim' it extended to 'abundant, flourishing, prosperous' (shèng).
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.