trapezoid and trapezium?
trapezoid the stress on the first syllable, trapezium the stress on the second syllable? is that right. and are they common to use in modern American English? what are they difference? interchangeable or they are different?
thank you very much!

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Trapesium is a super common shape. four straight sides, two parallel sides. Never heard of a trapezoid before. :) (British English speaker) "Trapezoid" seems to be some weird word for a general quadrilateral.

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Hi Michael,
yes, you are right about the stress patterns in those words.
but about the meaning, I should say that it is a bit confusing.

in American English, a trapezoid is a trapezium in British English and vise versa (a trapezium in American English is a trapezoid in British English) 😂😂😉😉

this is how the OALD9 tries to clarify the confusion.
this is the entry for 
trapezium:
1(British English) (North American English trapezoid) a flat shape with four straight sides, one pair of opposite sides being parallel and the other pair not parallel
2(North American English) (British English trapezoid) a flat shape with four straight sides, none of which are parallel

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Trapezoid is a common shape. I had to look up what a trapezium was. I doubt many people would know what that is.

Trap·e·zoid.    --    trapəˌzoid

Tra·pe·zi·um.    --    trəˈpēzēəm

I hope this helps!🍻