From the pages of Wasyu's Encyclopedia Tenchicca--
n.: In Chinese, the word Ten has the meaning sky or heaven, the word Chi meaning ground or earth; Mu means no or never while Yo means use or need. Together these four words translates to No Need for Tenchi or Tenchi is Useless; Pioneer adopts the former to be the title of the English dubbed version of Tenchi Muyo!
n.: In Japanese, Tenchi Muyo! can also mean upside down or this side up. Following this lead, Tenchi Muyo! can also imply life turned upside down, which quite accurately describes a typical day in the Masaki household.