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