Pro tanto is a Latin expression that translates to "for so much." In legal terms, it means that something is valid or enforceable only to a limited degree. There are several similar phrases or synonyms that can be used in place of pro tanto, including "to the extent of," "in proportion to," "partly," "in part," and "to a certain extent." These phrases all signify that something is only considered valid in certain circumstances, or that it is only applicable to a limited extent. It's essential to understand the use and meaning of pro tanto and its synonyms in legal language to ensure accurate understanding and interpretation of legal documents.