I had a look at the Constitution and the first ten amendments, the Bill of Rights. There are two guaranteed rights relevant to a jury trial. The Sixth Amendment guarantees the right to "a speedy and public trial, by an impartial jury of the State and district wherein the crime shall have been committed." The Fourteenth Amendment which describes "Citizenship Rights" says that a State may not deny "..any person within its jurisdiction the equal protection of the laws." The use of the phrase "jury of my peers" came much later in interpretation of the guaranteed rights.
The Bill of Rights was ratified in 1791. I wondered what the word "peer" meant to American citizens at the close of the 18th century. I consulted Noah Webster's remarkable work, An American Dictionary of the English Language which was published in 1828 in an edition of 2500 copies. I chose Webster over Samuel Johnson whose British masterpiece was published in 1755. Webster was a fierce patriot and resented the ignorance shown of American institutions in contemporary British dictionaries. He labored over his own magnus opus until his seventieth year, and managed a second edition in 1841 before he died at age 85. We have Webster to thank for the first documentation of true American vocabulary such as skunk, hickory and chowder. We can also thank Webster for some spelling simplifications such as music for musick, and plow for plough. Although Webster's dictionary was not yet in print, the drafters of the Bill of Rights used English as spoken in America, the same English that Webster was including in his 70,000 entry work.
Here is Webster's 1828 definition of peer, n.:
Do you think the rights guaranteed by the Sixth and Fourteenth Amendments would be stronger or more clear if peer were added?