自己走過的路再走一次
這是核心畫面最直接的樣子：腳印是你自己的，你照著它倒回去。
verb · B2
To go back exactly the way you came, usually because you are looking for something you lost or want to check what happened.
原路折返
核心畫面
One picture runs through the whole word: a line that already exists, and a second pass along it. Think of footprints in wet sand. The walk has been made; the marks are still there; now someone goes along them again, in the same order, looking as they go. Nothing new is being made. The value is in the second pass — you see what you missed, you find what you dropped, or you make the line clearer than it was. Change what the line is made of and you get every sense: your own footprints, another traveller's route, the traces a person left behind in records, or a pencil line on paper.
這個字可以想成同一個畫面：有一條線已經在那裡，而你沿著它再走第二次。想像濕沙上的腳印。路走過了，印子還在，現在有人照…更多收起
這個字可以想成同一個畫面：有一條線已經在那裡，而你沿著它再走第二次。想像濕沙上的腳印。路走過了，印子還在，現在有人照著同樣的順序再走一遍，而且一邊走一邊看。這裡不是在造新的東西。價值在於「第二次」：你看見第一次漏掉的、找回掉了的、或把線描得比原來清楚。把那條線換成不同材料，就得到這個字的每一種用法——自己的腳印、別人的路線、一個人留在紀錄裡的痕跡，或紙上的一條鉛筆線。From the word’s history
Retrace came into English from French retracer, from Middle French retracier. Read as its parts, it is re- (again) plus trace (to draw along or follow a mark), which is exactly the picture the modern senses share.
「retrace」是從法文 retracer 進入英文的，再往前是中古法文 retracier。拆開來看就是 re-（再一次）加上 trace（沿著痕跡描或走）。這個組合正好就是今天各個意思共用的畫面：痕跡已經在，你再走一次。
Wiktionary entry for retrace (etymology text supplied in this batch's evidence packet, source_ref kaikki:3f6f69a190036ae4:908868308:6952)
Three branches
別人留下的路線
腳印換成別人的。線還是已經存在的那一條，只是你不曾走過；差別在於你是用腳走，還是用資料把它重新畫出來。
verb · C1
To travel exactly the same route that someone else travelled before you, usually on purpose and in order to see what they saw.
重走別人走過的路線
紙上的線再描一次
把「路」換成「筆畫」，核心畫面完全不變：線已經在紙上，手再沿著它走一次。這是字面最貼近 trace 原義的一支。
verb · B2
To draw or go over a line that is already there a second time, usually to make it darker, clearer or more correct.
再描一次（線條）