Englishfor English speakers
over
Preposition
—
Something is over when it has finished, usually referring to an event.
When the movie was over we left the movie theater.
—
In a location above something.
He stepped over the dog.
—
From one side to the other.
They went over the bridge.
—
If you invite someone over, you invite them to your house.
They had him over for tea.
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A number divided by another.
Eight over two is four.
over
Noun
—
An over in a cricket match is six balls bowled from one end.
The captain told me I would have to bowl the next over.
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".
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In some schools, an A is a very high grade.
Ron got an A on his earth science test.
catalyst
Noun
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A substance that makes a chemical reaction happen faster. The catalyst is not changed by the process and can be used again.
—
A catalytic converter.
—
Someone or something that encourages progress or change, or helps it happen.
I hope the new CEO will be a catalyst for change.
Communication is a catalyst for peace.