Not really wanting to harp on this much, but as a word of advice: I think dictionary.com should not be accepted as an authority on the definition of English words. They are often very inaccurate, discard established conventional meanings in favour of dumbed-down retard newspeak.
I'd rather recommend something like dictionary.cambridge.org, or maybe a dusty old paper dictionary.
uk /ˈsel.ə.bət/ us /ˈsel.ə.bət/
not having sexual activity, especially because you have made a religious promise not to
Sexual activity includes masturbation.
Of course, celibacy is a western word. But according to my understanding, it is a good and faithful translation, in at least this context, for the Pali word brahmacariya.
I don't think it is a justifiable buddhist position to say that avoiding sexual relations with others, but habitually masturbating instead, is better than to engage in faithful sexual relations. And certainly it is not a mode of brahmacariya.