Actually, men didn’t buy wives, they got paid to take the woman off her parents’ hands traditionally (a dowry)
. But that’s besides the point. Certain aspects of marriage may have changed over the years (some for better, some for worse), however it has constantly never been between people of the same sex.
Contraception has distorted our view of marriage geatly. Nowadays, we see marriage as two people who love each other, have sex with each other, and want to spend the rest of their lives together (until they stop getting along at least). The contraceptive mentality has removed the procreative aspect from marriage. If you remove procreation from marriage, gay marriage becomes logical. When procreation is an aspect of marriage, gay marriage makes no sense. Until contraception, procreation was always intrinsically part of marriage, even marriages without the kind of love we associate with it today (like political royal marriages). This is why homosexual marriage wasn’t even a concept until recently (along with “homosexual” becoming a class of people, instead of homosexual acts simply being sins).
As for your dictionary definition, that just shows how the word “marriage” is used today, it doesn’t have any moral authority over what marriage should be.
This is like my second post ever, I hope it’s good!!