One way to hold this word: a single good mouthful, held out on someone's fingers. Not a meal, not a plate — one bite, and a bite worth having. That is why the word shows up wherever something small and pleasing is being handed over. Keep the same gesture and change what is in the hand, and you get the other use: one small, tasty piece of news passed to you across a desk.
可以想成一小口好料，捏在別人的指間遞過來。不是一餐，也不是一盤，就是一口，而且是值得吃的那一口。所以這個字總出現在「有人把好東西遞給你」的場合。手勢不變，只換掉手上的東西，就得到另一個用法：一小則好聽的消息，隔著桌子傳到你這邊。
From the word’s history
Wiktionary traces the word to Old English tid, meaning fond, tender or nice, plus bit, a morsel: a pleasing little piece. Both modern uses stay inside that phrase.
Wiktionary 記的是古英文 tid（討人喜歡的、好的）加上 bit（一小口），也就是「討喜的一小塊」。今天的兩個用法都還待在這句話裡面。
Wiktionary, "tidbit"
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