A tributary is a smaller river or stream that flows into a bigger one. Note the direction — it always runs in, never out.

A tributary is a smaller river or stream that flows into a bigger onetributary 是指流進更大河川裡的小河或小溪。Note the direction要注意方向——it always runs in, never out永遠是流進去，不會流出來。

The Han River is a tributary of the Yangtze; the water leaves the small river and joins the big one. Geography books use this word constantly, and so do news reports about floods and pollution, because what happens in a tributary ends up downstream in the main river.

The Han River is a tributary of the Yangtze漢水是長江的支流； the water leaves the small river and joins the big one水從小河離開，匯入大河。Geography books use this word constantly地理課本一直在用這個字， and so do news reports about floods and pollution報導水災和污染的新聞也是， because what happens in a tributary ends up downstream in the main river因為支流發生的事最後都會流到下游的主流去。

There is a second, older meaning, used as both noun and adjective: a tributary state or ruler was one that paid tribute — money, goods, or a formal gift — to a stronger power in exchange for being left alone. Imperial China's relationships with its neighbours are usually described in English as the tributary system, so Taiwanese students often meet this meaning in history before the river one.

There is a second, older meaning還有第二種比較古老的意思， used as both noun and adjective可以當名詞也可以當形容詞： a tributary state or ruler was one that paid tribute一個 tributary state（朝貢國）或 tributary ruler（藩屬統治者）就是會進貢的一方——money, goods, or a formal gift可能是錢、物品、或正式的禮物——to a stronger power in exchange for being left alone獻給更強大的一方，換取對方不來侵犯。Imperial China's relationships with its neighbours are usually described in English as the tributary system中國歷代王朝跟鄰國的關係，英文通常稱為 the tributary system（朝貢體系）， so Taiwanese students often meet this meaning in history before the river one所以台灣學生常常是在歷史課先遇到這個意思，才在地理課遇到河流那個意思。

The two senses share one picture: something smaller giving what it has to something bigger. As an adjective it can also just mean 'flowing in' — a tributary stream.

The two senses share one picture這兩個意思背後有同一個畫面： something smaller giving what it has to something bigger比較小的一方，把自己有的東西給比較大的一方。As an adjective it can also just mean 'flowing in'當形容詞時，它也可以單純表示「流進去的」——a tributary stream像 a tributary stream（一條支流）。