Stand still and turn until you are looking straight back the way you came. That is half a circle, 180 degrees, and the number alone is enough to name it. Everything else this word does keeps that half-turn and changes only what is turning: a board, a plan, or two things already sitting at opposite ends.
From the word’s history
Wiktionary gives the origin plainly: the noun is shortened from '180-degree turn'.
Wiktionary 直接寫著它來自 180-degree turn（一百八十度轉身），說話時只留下角度這個數字。
Wiktionary (kaikki dump, source_ref kaikki:3f6f69a190036ae4:1443795091:5368), supplied in the evidence packet
登入就可以看每一支怎麼連回核心畫面。
原始詞典資料3 筆記錄
以下是外部詞典記錄的用法，摘錄並精簡格式，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。
180noun
- 1
hobbieslifestylesportsAn instance of spinning 180 degrees, so that one is facing in the opposite direction.
- He did a 180 off the diving board.
- 2
The exact opposite.
- The friendly welcome was a 180 from what she had been expecting.
- As a result of his refusal, the employee was subsequently canned in 2015 on the basis of […] being boring […] In other words, it was a complete 180 from most employees who get fired for being too wild.
- 3
A complete change of direction or opinion.
- She used to like turnips, but she did a 180 and now hates them.
- Got so sick of crying, so just lately / When I catch myself, I do a 180
摘錄自 英文維基詞典 English Wiktionary，已精簡格式；依 CC BY-SA 4.0 授權使用，改動後的內容同樣以此授權提供。