Englishfor English speakers
knock
Noun
—
A sound from something hard hitting wood.
—
An impact.
knock
Verb
—
When you knock on something, you hit your knuckles onto it repeatedly.
She knocked on my door three times before I opened it.
—
When you knock something, you hit it, often accidentally.
down
Preposition
—
Toward the earth, away from the sky.
What goes up on earth must fall down.
—
Toward the bottom.
—
Towards a smaller price, number, amount, etc.
I'm going to buy a computer once prices go down.
down
Noun
—
Down is soft feathers or a covering of soft feathers.
That pillow is full of down.
a
Determinative
—
A is used when the following word could be any of a certain type.
Compare "A book I saw on the shelf" and "The book I gave you yesterday".
a
Noun
—
A is the first letter of the alphabet.
The letter "a" comes before "b".
—
In some schools, an A is a very high grade.
Ron got an A on his earth science test.
hurdle
—
verb
jump a hurdle
—
noun
a light movable barrier that competitors must leap over in certain races
—
noun
an obstacle that you are expected to overcome
the last hurdle before graduation
—
noun
(= vault)
the act of jumping over an obstacle