Picture an army pulling back. One small group does not go with it. They stay at the back, facing the people who are chasing, so everyone else can get clear. They are not trying to win — they are buying hours. Every use of rearguard in English comes back to that group and that job.
可以想成這樣一幅畫面：一支軍隊正在往後撤，有一小批人沒有跟著走。他們留在最後面，面對追上來的人，讓前面的大隊能安全脫身。他們的目標不是打贏，是替別人換時間。rearguard 後來的每一種用法，都還看得到這批人和這份工作的影子。
From the word’s history
The word is rear + guard, and its older shape says the same thing: Old French rereguarde, from rere 'behind' and guarde 'guard', Middle English rier garde. The name has always been simply 'the guard at the back'.
這個字就是 rear（後面）加 guard（守衛）。更早的形狀說的也是同一件事：古法文 rereguarde，rere 是「在後面」，guarde 是「守衛」，中古英語寫作 rier garde。從頭到尾，它的名字就是「後面那組守的人」。
Wiktionary, "rearguard"
登入就可以看每一支怎麼連回核心畫面。