Now, I know what you're thinking: 'mullet' refers to something like this:
Apparently the term has only been used in the hair cut sense since the early 1980's - in Canada at that period a popular choice for hockey players as well. I love the Chambers Dictionary (9th edition, 2003) entry for this:
Mullet: noun. a hairstyle that is short at the front, long at the back, and ridiculous all round.
It's funny to come across such humorous little editorials in a dictionary once in a while.
Perhaps for those of you trapped on a desert island in the 1980's and early 1990's, free from the ravages of popular culture, the word 'mullet' may bring to mind a species of fish:
That's not what I'm chasing down today folks. There's also a definition for mullet referring to a heraldic crest shape, and again, we need not concern ourselves with that here.
As it turns out, the term 'mullet' goes way back in carpentry and describes neither a hair style nor the dinner option.
noun. A piece of wood used for gauging the edges of a panel in frame and panel construction. The mullet piece is plowed with a groove by the same tool used to prepare the grooves in the frame members.
verb. Mulleting: gauging the edges of panels to fit the corresponding groove cut in the framing.
A picture explains all I think:
(Above image from T. Corkhill's The Complete Dictionary of Wood).
The modern dictionaries I have on my desk, Websters Unabridged and the Chambers Dictionary aren't much help here, making no mention of a woodwork-related definition for 'mullet'. George Ellis, in his 1908 work Modern Practical Joinery mentions the term, as does Middleton in his 1921 work Modern Buildings, Their Planning, Construction And Equipment Vol. 2.. William Stitt's work The Practical Architect's Ready Assistant (1819) also mentions mulleting a panel on page 121. Paul Hasluck's Cabinetwork and Joinery: Comprising Designs and Details of Construction, with 2021 Working Drawings and Twelve Coloured Plates (1907) mentions 'mulleting a panel' on page 221. All of those books are available online in digital format. To dig more deeply into the roots of this word, a look into the Oxford English Dictionary is really the only way to go (sorry Websters!). According to the O.E.D., def. 8 for 'mullet' indicates the word connects to the French word molet (around 1808) and even earlier to the French word moulet. Looking up molet in a 19th century French dictionary, I found:
MOLET.1 (mo-lè) s. m.Petit morceau de bois portant une rainure, dans laquelle le menuisier fait entrer les languettes d'un panneau pour en vérifier l'épaisseur.
That translates as, "Small piece of wood with a groove cut in, which the carpenter brought to the panel to check the thickness".
So, molet would be the obvious source for the English word 'mullet' (in the carpentry sense of the term), and as you can see, our ancestors clearly mangled the pronunciation in borrowing the word from French. I suspect that the word come into English as result of someone reading French, not hearing it, and not being a speaker of the language.
And what about the other root word 'moulet'? Again, an old French dictionary sheds light:
MOULET(mou-lè) s. m.Terme de menuiserie. Calibre de bois pour régler des épaisseurs.
Translation: "Carpentry Term. A piece of wood used as a caliper to adjust thickness".
Taking both molet and moulet back a little further, they both connect to the French word moule. In turn moule comes from the Latin word modulus, meaning 'little measure' and modulum, meaning 'measure, model'. From the same Latin root, and by way of French, we obtain the English words module, mould/mold, moulding/molding, mode, model, and, yes, mullet. Quite a wellspring.
I found the word hunt fascinating to say the least. Thinking about the use of a mullet as a gauging device, I do wonder though about the matter of using the same tool which plows the groove to make the mullet. Surely it is the case that repeated gauging by the block on slightly over-thick panels would render a certain amount of compression set with the block's wood grain, which would mean the gauge would then have a wider groove, and from there on would be consistently indicating a panel thickness slightly larger than the actual frame's groove(?). If the goal was to have the panel be a tight fit, I suppose that would work, though having an overly tight panel is a recipe for assembly woes. An interesting question. Does using such a gauging block make sense to you?