Formal:
* Obsolete: This word implies something is outdated and no longer in use.
* Archaic: This word suggests something is very old and no longer relevant.
* Superseded: This word means something has been replaced by something newer and better.
* Outmoded: This word implies something is no longer fashionable or in style.
* Deprecated: This word specifically refers to something that is no longer supported or recommended.
Informal:
* Out of fashion: This phrase implies something is no longer trendy or stylish.
* Has-been: This word refers to someone or something that was once popular but is no longer.
* Passé: This word implies something is outdated and no longer relevant.
* Out of date: This phrase means something is no longer current or up-to-date.
* Dead: This word is informal and indicates something is no longer popular or relevant.
To choose the best word, consider the specific context and what you want to emphasize.