It's a word in Portuguese. (Azinhaga)

The Japanese title looks like it's wordplay

The series title has no particular significance to the story. "Azumanga" is a portmanteau of the author's name "Azuma" and "manga", while "Daioh" comes from the magazine in which it was originally published, Dengeki Daioh. In the anime, "daioh" is mentioned during the next episode previews, used in context with the meaning "great king".