The pronoun anybody is always written as one word: Is anybody home? There isn't anybody in the office. The two-word noun phrase any body means “any group” (Any body of students will include a few dissidents) or “any physical body”: The search continued for a week despite the failure to find any body. If the word a can be substituted for any without seriously affecting the meaning, the two-word noun phrase is called for: a body of students; failure to find a body. If the substitution cannot be made, the spelling is anybody. Anybody is less formal than anyone. See also anyone, each, they.