What’s petty about petty officers

Award-winning mystery author, P.D. James, recently wrote a sequel to Jane Austen’s signature book, Pride and Prejudice.
James calls her novel, Death Comes to Pemberley, and as Austen fans know, Pemberley is the name of Mr. Darcy’s estate.
Death Comes to Pemberley takes place a few years after Elizabeth Bennet and Fitzwilliam Darcy marry. The story involves an army officer found dead in Pemberley’s woods.
A man discovered with the officer’s body is placed under police guard at Pemberley House. James names the two policemen as Headborough Thomas Brownrigg and Petty Constable Mason. Their stated ranks were unfamiliar to me, and although my cousin, Jim Auld, was a petty officer in the Canadian Navy (RCNVR) during the Second World War, I’ve never wondered about the curiously named rank of “petty officer.”
The word petty has been in English since 1573. As used by the military, it doesn’t mean “unimportant” or “trivial.” It is, rather, the phonetic spelling of the French petit, and in the Navy, equals “subordinate.” That is, petty officers are subordinate to commissioned officers like captains, commanders, and admirals.
A petty officer, therefore, is a “minor” officer, his rank corresponding to that of a non-commissioned army officer — sergeant or warrant officer. This meaning has existed in Britain since 1577 and in Canada since our own navy was established in 1910.
The Dictionary of Contemporary Usage notes that the spellings petit and petty were once interchangeable, adding that the French spelling remains in English in expressions like petit mal (mild epilepsy), petit point (a type of embroidery), petit fours (tiny frosted cakes), and petit pois (small peas).
Spelled petty, the word shows up in petty larceny, petty cash, petty theft, and so on.
Although Canadians don’t hear of petty constables, Oxford says this rank existed in England as early as 1597. At that time, a constable was defined as, “an officer of the peace,” a definition that remains valid.
Constable is Middle English from the Old French cunestable (count of the stable).
As for that other guard at Pemberley, Headborough Thomas Brownrigg, his rank — used since 1440 — also means petty constable. However, headborough’s original meaning referred to the head, or leader, or a self-governing town, a freeborough. So, in James’s book, that petty constable known as a headborough is the chief petty constable. Interestingly, the navy has chief petty officers.
Petty is also used as an expression of contempt — petty outlook, petty complaint. The source is still petit.
English, our every-growing, ever-changing tongue, still reaches back to bygone times for much of its vocabulary.
P.D. James is an excellent author who writes books you don’t want to put down. But, in my opinion, she misses the boat with Death Comes to Pemberley. I never felt I was back with Elizabeth Bennet and Mr. Darcy of Pride and Prejudice.
I’m apparently alone in that opinion. Reviewers from such prestigious journals as the Guardian, London Evening Standard, Washington Post, and the Economist, believe James has “captured the cadence and storytelling quirks of Austen” (Globe and Mail).