1.leaf的基本意思是“树叶”,指生长于植物的枝杈之上的植物的一部分;也可指书本的一“页”或桌子的“折面或活面”。leaf还可指一种特殊的“金属薄片,金箔”。
2.leaves作“树叶”解时,其后可接on来表示“在树上的叶子”,而不接of。
3.come into leaf和in leaf中的leaf都用单数形式。

come into〔be〕 in leaf
长叶子,生满叶的,绿叶满枝的 grow leaves;being covered with leaves
I love this time of year when all the trees are coming into leaves.我喜欢一年中的这个时候,所有的树木都在长叶子。
The trees will soon be in leaf.树木不久都要绿叶满枝了。

take a leaf from〔out of〕 sb's book
以某人为榜样 copy sb;act or behave in a similar way to sb
You should take a leaf out of your brother's book and study more.你应该学你哥哥的榜样,多学点知识。
If you want to buy a house, you should take a leaf out of my book and start saving money.如果你想买房子,你就应该学学我的样子,开始攒钱。

turn over a new leaf
掀开新的一页,重新开始,改过自新 begin a new course of improved behaviour, habits, etc.
He promised to turn over a new leaf and study harder.他保证重新开始,更加努力地学习。
I've decided to turn over a new leaf and do lots of exercise from now on.我已决定重新开始,从现在起多锻炼。
He decided to turn over a new leaf. He would live simply and regain the respect of his family.他决定改过自新,艰苦朴素,重新得到家人的尊敬。

Leaves fell off.叶子落了。
The leaves turn brown in autumn.树叶在秋天变成褐色。
It was autumn and the leaves were yellow.已经是秋天了,树叶变黄了。
I took away the leaves in the gutters.我清除了檐槽中的树叶。
The wind became furious, tearing leaves off trees, carrying great volumes of dust before it.风变得狂暴起来,把树叶纷纷吹落在地,刮起大量尘土。
They live in a frail shelter of leaves.他们居住在一个用树叶搭成的不结实的棚子里。
Several leaves had been torn out of the novel.这本小说已被撕掉了几页。
Slowly, she turned the leaves of the beautiful old book.她慢慢地翻动那本漂亮的旧书的书页。
They needed three gold leaves.他们需要三张金箔。
We put two extra leaves in the table for the dinner.为了这次晚宴,我们给餐桌上加了两块活动面板。
Pull out both leaves of the table.把桌子的两块活动面板都拉出来。

leaf偶尔也可用作动词,与together连用,表示“匆匆阅读”。例如:
Waiting to see the doctor,Jim was too nervous to read properly, so he just leafed through some old magazines that were kept in the waiting room.吉姆在等医生看病时,紧张得无法看书,所以只是翻翻放在候诊室的几本旧杂志。

［词源］  ＜中古英语lefe＜古英语leaf(叶)