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| Subject | English | Japanese |
| obs. | n vs crowning a boy with a traditional cap for the first time at a coming-of-age ceremony | 加冠 |
| phys. | first-order phase transition | 一次相転移 (いちぢ・そうてん'い) |
| gen. | n first year pupil in junior middle school | 中１ |
| gen. | n first year pupil in junior middle school | 中一 |
| phys. | phase transition of the first kind | 第一種相転移 (だいいっしゅ・そうてん'い) |