"Not for publication" is a phrase that is commonly used to indicate that certain information or materials are not meant to be shared publicly. There are several synonyms for this phrase that can be used interchangeably in different contexts. For example, "confidential," "secret," "private," and "proprietary" are all commonly used as alternatives to "not for publication." These words all connote a sense of exclusivity and are meant to indicate that the information or materials in question are not meant for widespread dissemination. Additionally, phrases like "off the record" and "not for public consumption" can also be used to convey a similar idea. Overall, it is important to choose the appropriate synonym depending on the specific context and audience.