名詞 eighteen:

1. the cardinal number that is the sum of seventeen and one
   同義詞：18, XVIII

形容詞 eighteen:

1. being one more than seventeen
   同義詞：18, xviii

1. The age of majority is eighteen.
   成年的法定年齡是18歲。
2. A pension is not usually one of the preoccupations of an eighteen year-old!
   一個(gè)十八歲的人通常是不會(huì)老惦著養(yǎng)老金的！
3. I was eighteen on my last birthday.
   我已經(jīng)過了18周歲了。
4. The champion is leading by eighteen seconds.
   該冠軍領(lǐng)先十八秒。
5. She dolled herself up as though she was a girl of eighteen.
   她打扮得花枝招展，好像是個(gè)十八歲的姑娘似的。
6. My daughter is eighteen years old and has grown into a beautiful lady.
   我的女兒十八歲了，已經(jīng)長(zhǎng)成為美麗的淑女。

eight.een

n.（名詞）
The cardinal number equal to 7 + .
十八：等于7+的基數(shù)
The 8th in a set or sequence.
第十八：一組或一列順序中的第十八個(gè)

來(lái)源：
Middle English eightetene
中古英語(yǔ) eightetene
from Old English eahtatône * see oktô(u)
源自 古英語(yǔ) eahtatône *參見 oktô(u)

【引伸】
eighteen.
adj.（形容詞）
pron.（代詞）