1.horse的基本意思是“马”,尤指未阉过的成年公马。引申可表示“骑马的军人,骑兵”,还可指撑衣服用的架子,即“衣架”。用于俚语可指“海洛因”。
2.作“马”解是可数名词,在句中有时可用作定语; 作“骑马的军人,骑兵”解是集合名词,不可数,只有单数形式,但可与单数或复数动词连用。

Horses are useful animals.马是有用的动物。
A horse can carry a heavy burden.马能负重。
The horse dashed down the hill.马从山上急冲而下。
The horse became frightened and ran away.那匹马受惊吓跑了。
My horse fell and rolled over on me.我的马倒下来滚在我身上。
His horse rides well.他的马好骑。
The horse responded well to his control.这匹马很听从他的指挥。
These horses remained together for most of the race.在比赛大部分过程中,这些马都挤在一起。
The horse suddenly reared up and threw me off.马忽然用后腿直立起来,把我摔下马背。
The horses were feeding quietly in the field.马群在田野里静悄悄地吃着东西。
Are you going to race your horse at Newmarket next week? 你要让你的马参加下周在纽马克特的赛马会吗?
The old man likes raising rabbits, chickens, dogs and horses.这个老人喜欢养兔子、鸡、狗和马。
We stopped to rest the horses.我们停下来让马休息一下。
We ride our horses in the park each morning.我们每天早晨在公园里骑马。
Don't make your horse go so fast on this rough ground, you're riding for a fall.别让马跑那么快,路面这么不平坦,你这是在冒险。
They rode 30 li on the horse.他们骑马走了30里。
The enemy had five hundred light horse.敌军有500名轻骑兵。
He risked $100 on the horse race and lost it all.他下了100美元的赛马赌注,全输光了。

horse, steed
这两个词都有“马”的意思,其区别是:horse是马的总称,特指未阉过的成年公马; steed指战马,常用于文学作品中。例如:
He jumped on his steed and rode off at a gallop.他跃上战马,疾驰而去。
A knight rode on his richly caparisoned steed.一个骑士骑在他装饰华丽的马上。

［词源］  ＜古英语hors(马)