To and fro means moving one way and then back again, over and over: a swing, a boat on waves, a person walking up and down a room while worrying. 'Fro' is an old word for 'back' that survives nowhere else in modern English — it lives only inside this phrase, which is why it looks so strange on its own.

To and fro means moving one way and then back again, over and overTo and fro的意思是朝一個方向移動、然後又移回來，一遍又一遍： a swing, a boat on waves, a person walking up and down a room while worrying像是鞦韆、海浪上的船、或是一個人擔心地在房間裡走來走去。 'Fro' is an old word for 'back' that survives nowhere else in modern English'Fro'是一個代表「回去」的古字，在現代英文裡除了這個片語以外已經不存在了—— it lives only inside this phrase它只活在這個片語裡， which is why it looks so strange on its own這也是為什麼它單獨看起來這麼奇怪的原因。

Most often it comes after a verb of movement: the branches swayed to and fro, she rocked the baby to and fro. It feels a little old-fashioned and a little literary; in ordinary conversation people are more likely to say 'back and forth', which means exactly the same thing.

Most often it comes after a verb of movement它最常出現在表示移動的動詞後面： the branches swayed to and fro, she rocked the baby to and frothe branches swayed to and fro（樹枝來回搖曳）、she rocked the baby to and fro（她來回搖著寶寶）。 It feels a little old-fashioned and a little literary它給人一種有點老派、有點文學的感覺； in ordinary conversation people are more likely to say 'back and forth'在一般對話裡，人們比較常說'back and forth'， which means exactly the same thing意思完全一樣。

With hyphens, to-and-fro can work as a describing word before a noun (a to-and-fro motion) or as a noun for the whole business of going back and forth — and that noun often means an exchange of words rather than real movement: after a lot of to-and-fro between the two lawyers, they agreed. That last use is common in news and business writing, where the to-and-fro is the arguing, the emails, the offers going one way and answers coming back.

With hyphens, to-and-fro can work as a describing word before a noun (a to-and-fro motion)加上連字號，to-and-fro可以當形容詞放在名詞前面（a to-and-fro motion，來回的動作）， or as a noun for the whole business of going back and forth也可以當名詞，指整個來回往返的過程—— and that noun often means an exchange of words rather than real movement而這個名詞用法常常指的是言語上的交鋒，不是真正的移動： after a lot of to-and-fro between the two lawyers, they agreedafter a lot of to-and-fro between the two lawyers, they agreed（兩位律師來回交涉了很久之後，他們達成了共識）。 That last use is common in news and business writing這最後一種用法常見於新聞和商業寫作， where the to-and-fro is the arguing, the emails, the offers going one way and answers coming back那時候to-and-fro指的是爭論、往來的郵件、一方提出條件、另一方回應的過程。