曾

Bottom rectangle is the 曰 radical (Kangxi #73), originally the cauldron base of a steamer. The dictionary files 曾 under 曰 for both readings — same shape, same radical, only sound and sense diverge.

Same glyph as the céng reading — top 8 strokes are the fused steamer body (丷 cap = rising vapor, middle = chambered pot). The zēng reading is older: 'layered, doubled,' which is why it labels kinship two generations removed (great-grandfather = doubled grandfather). The 'once / formerly' sense (曾) is a later borrowing on the same graph.