It must have been quite hard, being a lawyer in the Middle Ages in England. Originally, all your law books would have been in Latin. Then, in the 13th century, they start being written in French. Then along comes English. Lawyers had a problem. Should they they describe the issue using an English word or opt for the equivalent word in French or Latin? And would the words be equivalent anyway?... The lawyers thought up an ingenious solution. They would use both.
-- From "The Story of English in 100 Words" by David Crystal
Legal pairs include will and testament, good and chattels, null and void, aided and abetted, and the triplet: give, devise, and bequeath. Can you think of others?