1.grass的基本意思是“草”,指各种草的总称,通常长有绿色的叶子,可以被牛、羊等动物食用的草,也可指铺设草坪用的草,还可指一片长满草的区域,即“草地,草坪,牧场”。grass还可用于指“禾本科植物”,此时多用来指不同种类的“草”。有时, grass还可指向警察告密的人(自己往往是罪犯),即“告密者”。引申可指“大麻”“基层群众”。
2.grass作“草”“草地,牧场”解时多用作不可数名词,而作“禾本科植物”解时多用作可数名词。

as green as grass
少不更事,无生活经验 too young, having no experience
That lad appears to be very proud, but actually he is still as green as grass.那个小伙子似乎很骄傲,但实际上他还很无知。

cut one's own grass
自食其力 live depend on oneself
They make their children cut their own grass.他们让子女们自食其力。

put out to grass
退休,不再从事工作 no longer work
▲put sb out to grass
Some of these old judges are nearly 80, you know; it's time they were put out to grass!你知道,这些年事已高的法官中有的已经近80岁,他们该退休了!

Cattle eat grass.牛吃草。
Sheep live on grass.羊靠青草生活。
The grass is in need of cutting.这草需要割了。
The air was full of butterflies, a sweet fragrance rose from the wild grass.空中蝴蝶飞舞,野草散发着芳香。
We sat down on the dry grass with our backs to the wall.我们坐在干草上,背倚着墙。
The snake glided smoothly through the tall grass.那条蛇轻快地从草丛中穿过。
My clothes were damp from walking in long grass.在高高的草中行走,我的衣服都湿了。
They need evergreen grass to dot the square.他们需要常绿的草点缀广场。
Beneath them the earth was naked of grass.在他们脚下是寸草不生的土地。
The rain had cleared the air, and the grass smelt fresh and sweet.雨后空气洁净,草地散发出清新芬芳的气息。
He studies grasses.他研究禾本科植物。
He hid behind some high grasses.他躲在一些高大的禾草后面。
What you see in the paddy field is a grass.你在稻田里看见的是一种草。
This kind of grass grows apace.这种草长得很快。
There was an attractive arrangement of dried grasses in the vase.瓶里插了一些很好看的干草。
Keep off the grass.勿踩草坪。
People who walk on the grass are liable to a fine.在草坪上行走要受罚。
Half of the farm is grass.这个农场的一半是草地。
He was once a professional grass.他曾是一个靠告密为业的人。
The grass has tipped off everything to the police.那个眼线已把所有情况都告诉了警察。
Those people are smoking grass.那些人正在吸大麻。
It is evident that the mayor is inclined to keep in touch with the grass roots.显然,这位市长愿意时刻和基层保持接触。

grass, herb, weed
这三个词的共同意思是“草”。其区别是:grass指有益的草,如可供马、牛、羊等牲畜吃的牧草或人们铺设草坪用的草; weed指妨碍其他植物良好生长的杂草。例如:
She spent the whole afternoon pulling up the weeds in the flowerbeds.她花了整整一个下午拔去花坛中的杂草。
herb则指做药或香料的草。例如:
No herb will cure love.相思病无药可治。
下面两个短语意思相反:
let the grass grow under one's feet
让时间白白浪费
let no grass grow under one's feet
不浪费时间
下面两句含义有所不同:
She is sitting on the grass.
她坐在草中。(草长得矮,她可以被看见)
She is sitting in the grass.
她坐在草中。(草长得高,她无法被看见)

［词源］  ＜中古英语gras＜古英语græs(草)