增添
zēngtiān · HSK 7
increase
➕ 增 (increase) + 添 (add) = pile more on top; both halves mean to add
增 — earth 土 + 曾 (phonetic, 'layer/repeat')
A semantic-phonetic compound: 土 ('earth') gives the meaning, while 曾 supplies the sound and hints at 'layered, piled up.' The original sense was piling earth higher and higher, which generalized to 'increase, add to.' 曾 itself depicts a tiered steamer, reinforcing the idea of stacking.
添 — water radical 氵 + 忝 (phonetic)
添 is a phono-semantic compound. The water radical 氵 hints at the meaning 'to add water, to pour in more,' while 忝 supplies the sound. From the literal sense of topping up liquid, it broadened to mean 'to add' or 'to append' anything.