The linked dictionary entry is a perfect example of redefintion of the language under pressure of same sex "marriage" activists. The Oxford Advanced Learners Dictionary, fourth edition from 1989, which I have in my bookcase, defines
marriage - legal union between a man and a woman as husband and wife"
man - adult male human being
woman -adult female human being
Male - of the sex that does not give birth to ofspring.
Female - of the sex that can give birth to children or produce eggs.
gender - sexual classification; sex: the male and female genders.

So you are truth, there is nothing about "gender" but it is about sex!

The same it is in the Czech language. I tried put Czech definitions here, but it was deleted. So you can find it in The Czech Dictionary .

I insist on a marriage is something principally diferent than a homosexual union. It is principally different because it can procreate offspring.
I don't say that homosexual partners should not live in a union. But it is called a registered partnership.
I can't accept situation that is for example in France now. There is banned and can be punished to use in legal documents terms "mother" and "father". And it starts with using word marriage for homosexual partnership.