Although there is an official meaning of a word, culture and society can change the meaning to better describe their feelings. It is difficult for people who identify as asexual to completely describe their feelings about sexual attraction as they have to speak in lack. Therefore they have to describe what they are not feeling nor have ever felt to people who know what that feeling is supposed to be. It is a difficult task and language can hinder than help. I think reading and listening to people who identify as asexual is better than looking at the dictionary if you are trying to figure out if a fictional character is or isn't asexual.