Binding; have legal force or force; Legally sufficient. For example, a valid contract is a contract that has been performed in compliance with all necessary legal formalities and is binding and enforceable by the persons who performed it. See the full definition of validity in the English Language Learners VALID dictionary. An act, deed, will and the like that have received all the formalities prescribed by law is considered valid or legally valid. Synonyms/similar words: credibility, rigor, validity, rigor, convincing.