long是“长”,
tooth是“牙”,
long in the tooth是什么意思?
解答：
long in the tooth年纪大
“long in the tooth”的起源和马有关。马儿过了壮年，咀嚼能力就会衰退。咀嚼能力退化的标志是牙龈萎缩，牙根显露出来，从而使得马牙显得特别长，因此人们通过检查马牙长短来判断马的实际年龄和相应的价值。所以“long in the tooth”就是指“上了年纪，年纪大”～
例句：
She's a bit long in the tooth for such a romantic role. 演这样一个具有浪漫色彩的角色，她年纪有点太大了”
拓展知识：
有个成语叫“马齿徒增”，意思是“空有年岁增长而学业或事业没有长进”，可以翻译成“to be long in the tooth with nothing accomplished”
虽然tooth是“牙齿”意思，但在一些表达中却诠释着不一样的意境~
1.fight tooth and nail
释义：
to try very hard to get something you want
竭尽全力
例句：
We fought tooth and nail to get the route of the new road changed.
我们奋力抗争，争取改变新修道路的路线。
2.get your teeth into sth
释义：
to deal with something or become involved in something with great energy and enthusiasm
专注于
例句：
I'm so bored at work, I wish they'd give me something I could really get my teeth into.
我很厌倦工作，我希望他们能给我一件我能真正潜心去做的事。
3.in the teeth of sth
释义：
If something happens or is done in the teeth of difficulties, the difficulties cause problems but do not stop it.
违抗；不顾
例句：
The road was built in the teeth of fierce opposition from the public.
这条道路是在公众的强烈反对下修起来的。
4.set sb's teeth on edge
释义：
If something, especially a noise, sets your teeth on edge, it annoys you very much.
（尤指噪声）使（某人）非常恼火
例句：
That DJ's voice really sets my teeth on edge.
那位电台音乐节目主持人的嗓音的确使我很不舒服。
