One way to hold this word: a flat panel that sits just under the chin and lies across the chest. That patch of the body is the whole idea. Tie a cloth there and it catches the food a baby drops. it onto a pair of overalls and it becomes the square with a pocket on it. Pull a numbered square over your shirt at a race and it becomes the thing strangers read you by. Even an animal born with one white patch there gets described as wearing one. The material changes, the job changes, the place never does.
From the word’s history
Wiktionary records that bib was first a verb meaning to drink heartily, from Middle English bibben, either from Latin bibo or simply imitating the sound. It then suggests, without certainty, that the clothing sense came either from wearing the cloth while drinking or from the cloth drinking up what was spilt.
維基詞典說 bib 最早是動詞，中古英語 bibben「大口喝」，可能來自拉丁文 bibō（喝），也可能只是模擬聲音。至於為什麼變成衣服，它用的是推測的語氣：可能因為喝東西時圍著它，也可能因為這塊布會把灑出來的東西「喝掉」。這條線索有趣，但來源自己也說不確定。
Wiktionary, "bib" (etymology 1)
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