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A chin-up is a gym exercise. You hang from a high bar, then pull your body up until your chin is higher than the bar, then you go down slowly and do it again. In the strict version, your palms face toward you. Though actually, in casual gym talk some people use chin-up for any pull to the bar; careful trainers keep it apart from a pull-up, where the palms face away. The name is just chin plus up: you have not finished the move until the chin clears the bar. People named this exercise later than the pull-up, and that older name helped shape this one. It is gym English, not formal writing.
引體向上（手心朝自己、拉到下巴過槓的那種；手心朝外的多叫 pull-up）
組成From chin + up, but not built from a verb the way pull-up is. Named later than pull-up, with influence from that name; the muscle-up is another later variation of pulling yourself up.
原始詞典資料1 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
chin-upnoun/ˈtʃɪn.ʌp/
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hobbieslifestylesports(US) An exercise done for strengthening the arms and back, in which one lifts one's own weight while hanging from a bar. It can be defined more restrictively on criteria like the arms starting at lock-out, or the chin requiring contact with the bottom of the bar, or touching the neck to the bar. Palms may be facing in any direction.
- Compare the actions of the humerus during the performance of a chin-up with supinated grip with those during the performance of a chin-up with pronated grip. Are the chin-ups alike or different with respect to muscle involvement?
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。