pay back是「償還」還是「復仇」？

(1) pay back即repay what you owe，指「償還」，例如：

Will you lend me $1,000? I will pay you back next month.

借我1000元好嗎？我下個月還給你。
(2) pay back指repay someone for a kind act he or she has done，指「回報」，例如：

It was so nice to spend the weekend with you and your family. We'll pay you back when we've got a home of our own.

與你全家度周末，非常愉快。我們有了自己的家後，一定回請你們。

(3) pay back又為punish somebody who has done something bad to you，指「報復」或「懲罰」，例如：

We'll pay them back for their insults one day.

總有一天，我們會報復他們的冒犯。
(4) 再介紹一個與pay back（報復）近似的說法：

pay (a person) back in one's own coin即to treat a person in the way that he or she has treated you，指「以其治人之道，還治其人之身」，例如：

Since she refused to help me, the next time she asks me for a favour I will pay her back in her own coin.

既然她不肯幫我，下次她求我時，我當然也不幫她。

讀者Eva來電郵問，書中寫a shoe shop，但店舖裏有很多鞋，是否應寫shoes shop？

Shoe shop是名詞詞組，前面的shoe是名詞修飾語，表示shop的性質。此種情下，shoe毋須加s；同類的例子有：orange juice、childcare、animal trainer等。