A legal doublet is a standardized phrase used frequently in English legal language consisting of two or more words that are irreversible binomials and frequently synonyms, usually connected by "and", such as "null and void".
The order of the words cannot be reversed, as it would be seen as particularly unusual to ask someone to desist and cease or to have property owned clear and free, when these common legal phrases are universally known as cease and desist and free and clear.
The doubling—and sometimes even tripling—often originates in the transition from use of one language for legal purposes to another: in Britain, from a native English term to a Latin or Law French term; in Romance-speaking countries, from Latin to the vernacular.
In other cases the two components have differences which are subtle, appreciable only to lawyers, or obsolete.
Doublets may also have arisen or persisted because the solicitors and clerks who drew up conveyances and other documents were paid by the word, which tended to encourage verbosity.