釋義：

Long：長的，tooth：牙齒；字面來看呢，long in the tooth是牙齒長的意思；

In english：Old in age. Mostly used when referring to people or horses.英文里指的是年紀大，一般指的是人或者一匹馬；

來源：

This phrase originates from horses, or more specifically, it comes from one’s ability to discern a horse's age simply by looking at their teeth. 這個俚語與馬有關。有的人只是看下馬的牙齒，就可以判斷出馬的年齡。The longer the teeth, the older the horse. 牙齒長，年紀大。Thus, this phrase is used to describe how someone or something is long in years.所以這個俚語就用來被描述一個年紀大的人或者事物。While the phrase apparently began with horses, it eventually was applied to describe the age in humans too, among other things.雖然這個詞剛開始用來描述馬，但是最終也用來指代人或者其他事物；

舉例：

1.家里的電腦已經(jīng)用了50年了，很老了：

The desktop was getting long in the tooth.

那個臺式機是越來越老了。

2.試衣服時候試穿了一件顯老的衣服：

Don't you think you're a little long in the tooth for it?

你不覺得你穿這件衣服年齡有點大了嗎？