hun‧dred /ˈhʌndrəd, ˈhʌndrɪd/ number, noun (plural hundred or hundreds)
[Language: Old English]

1. the number 100:
The tree was probably a hundred years old.
two/three/four etc hundred
I make nine hundred dollars a week.
a journey of 15 hundred miles
hundreds of people/years/pounds etc
Hundreds of people were reported killed or wounded.

2. a very large number of things or people
a hundred
They’ve had this argument a hundred times before.
hundreds of something
He’s had hundreds of girlfriends.

3. a/one hundred percent spoken
a) completely:
I’m not a hundred percent sure where she lives.
b) British English completely well:
I’m still not really feeling a hundred percent.

4. give a hundred percent (also give a hundred and ten percent) to do everything you can in order to achieve something:
Everyone on the team gave a hundred percent.

5. [countable] a piece of paper money that is worth 100 dollars or 100 pounds
—hundredth adjective:
her hundredth birthday
—hundredth noun [countable]

[TahlilGaran] Dictionary of Contemporary English ▲

hundred
number
Using numbers
Day, month, minute, mile, kilo etc are always SINGULAR when used (with a number) immediately before a noun: ‘a six-minute wait’, ‘a ten-second silence’, ‘a five-mile race’.
My travel agent had arranged a 6-day coach tour.
The company provides a three-month training course.
Compare: ‘We waited for thirty minutes: ‘We had a thirty-minute wait.’
When you say 100, 1000 etc , or write these numbers in words, use a hundred, a thousand (WITH a ):
The palace was build a thousand years ago.
Compare: ‘The palace was built 1000 years ago.’
For emphasis or to be exact, it is possible to use one instead of a :
I am one hundred percent against the idea.
After a/one/five/twelve etc , the words hundred, thousand, etc are always SINGULAR and are NOT followed by of :
Five hundred children are born in the city every day.
More than three thousand people were there.
Similarly, of is NOT used after 100, 250, 3000 etc:
If you kill 200 whales a year, they will soon disappear.
Hundreds (of), thousands (of) etc are used only when you give a general idea of how many or how much: ‘There were hundreds of stars in the sky.’ ‘They’ve spent thousands (of pounds) on improvements to the house.’
Use and between hundred and the next number. (In American English, and is often omitted, especially in formal styles.)
BrE The club has about a hundred and thirty members.
AmE The club has about a hundred (and) thirty members.

[TahlilGaran] Dictionary of Common Errors ▲

hundred
ˈhʌndrəd
See: by the dozen or by the hundred or by the thousand

[TahlilGaran] English Idioms Dictionary ▲