Sport / Sports

I don't get how to use this word: sport. I have looked up many dictionaries but I don't get the word usage.

http://dictionary.reference.com/search?q=sports

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adj. or sports

1. Of, relating to, or appropriate for sports: sport fishing; sports equipment.
2. Designed or appropriate for outdoor or informal wear: a sport shirt.

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1. I have a sport shirt. (Why is 'sport' singular here?)
2. These are sports equipment. (Why is 'sport' plural here?)

3. I have a sport car. (If this is incorrect, why? #1 is correct?)
4. I have a sports car. (Why does it have to be 'sports'?)

Also, I found this in a dictionary:

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sports car (AmE also sport car) noun a low fast car, often with a roof that can be folded back

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5. I don't understand. So for AmE it is 'sport car'? And for North American english it is 'sports car'? If so, how do you know if 'sport' is plural or not?

6. For the adjective 'sport', I don't understand why sometimes it is plural and sometimes it is singular. Can you explain that to me? Thanks.

7. SUV: Sport Utility Vehicle. (Why isn't 'sport' 'sports'?)

1. a sport shirt. (A shirt for playing a sport.)
2. a sports shirt. (A short for playing sports.)

Both are synonymous in my dialect.

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Originally Posted by jack

So for AmE it is 'sport car'? And for North American english it is 'sports car'? If so, how do you know if 'sport' is plural or not?

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Please note, North American English is American English. The USA is in North America.;-)

Thanks.

What does the dictionary mean by this:
1. sports car (AmE also sport car) noun a low fast car, often with a roof that can be folded back. (What does the dictionary mean by AmE 'sport car'?)

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Originally Posted by jack

Thanks.

What does the dictionary mean by this:
1. sports car (AmE also sport car) noun a low fast car, often with a roof that can be folded back. (What does the dictionary mean by AmE 'sport car'?)

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I've always heard and said "sports car". I don't why the dictionary says that "sport car" for American English.

There's a lot more for "sports car" than "sport car". Maybe it's regional.