One way to hold this word: a line kept clean all the way back. Nothing was added from outside, generation after generation, and what comes out at the end is an animal built for one thing — speed — and built for it. The word carries both halves of that picture: where the thing came from, and how easy it makes the hard thing look. Move the picture onto a person and only the second half is really meant.
可以想成一條從頭到尾都沒混過的血統線。一代一代都沒有加進別的東西，最後養出來的，是一匹為了一件事而生的馬——速度——而且一眼就看得出來。這個字同時帶著畫面的兩半：東西是從哪條線來的，以及牠把難事做得多輕鬆。把這個畫面移到人身上時，真正要說的通常只剩後面那一半。
From the word’s history
The Wiktionary entry supplied in this packet records the word simply as thorough + bred — bred all the way through.
本批資料的 Wiktionary 條目只寫了一句：thoroughbred 來自 thorough 加 bred。thorough 是「徹底、從頭到尾」，bred 是「被養育出來的」，合起來正好就是核心畫面。
Wiktionary entry supplied in evidence packet (kaikki:3f6f69a190036ae4:1128414636): `From thorough + bred.`
登入就可以看每一支怎麼連回核心畫面。