There are several synonyms for "unwritten agreements" depending on the context of the use of the term. In legal terms, the phrase could be replaced with "implicit contract", "verbal agreement", or "tacit understanding". In business, the terms "gentleman's agreement", "nod-and-wink understanding", or "handshake agreement" can be used. Similar phrases such as "unspoken contract" or "implied pact" are also good alternatives. However, it is important to note that while these terms may be used interchangeably, they may come with different legal implications. Therefore, it is always essential to consider the context and the legal implications of each term when using them.