Perhaps it would be less puzzling if the sentence were "Το ορθογώνιο δεν έχει μόνο τρεις γωνίες".
I definitely agree with you, my friend
I agree, but I also believe that it would sound much more natural to say:
"Rectangles don't have [only] three angles."
"three corners" can we include?
A rectangle has more than three corners, this sentence does not make sense.
Maybe it would better to say ' the rectangle does not have five angles ' as I think from the comments posted we know it has three, plus another one.
Ορθογώνιο. I remember the word orto/ορθο as meaning more/several. Which means there can be n(very many) angels/corners in a ορθογώνιο.
a rectangle doesn't have three corners was not accepted 2/9/2021