A
璧 is a flat jade disc with a hole in the middle. Two half-discs fitted back into a full circle are a
合璧, so the word praises different things joined into one fine whole:
中西合璧 'a blend of Chinese and Western',
珠联璧合 'a perfect match'. Old astronomy said
日月合璧 when the sun and moon rose together like the two halves of one disc.
