My brother's wife's mother, set like a dictionary word
Three lines of heavy serif type spell out a relationship as a full sentence, set exactly like a dictionary headword, because there's no English noun for her at all.

MY BROTHER'S WIFE'S MOTHER runs across three lines of heavy black serif capitals, filling the chest the way a single word usually does. Underneath it, small and italic: noun.
The joke is entirely in the typography. The sentence itself is just true.
Why print a whole sentence like it's one word?
Because there isn't a word, so the sentence is doing a word's job, and the type says so.
English has terms for a spouse's parent, a sibling's spouse, even a spouse's sibling's spouse — but stack three relationships and the vocabulary runs out. Setting "my brother's wife's mother" in the same heavy capitals and centred layout you'd use for a single noun borrows the authority of a dictionary entry for a phrase English simply didn't let become one. The mismatch between the grand typographic treatment and the length of the actual words is where the print does its work.
Why does labelling it "noun" make it funnier than just complaining about the gap?
Because a label claims something has already been settled, and here nothing has.
A caption that said "there's no word for this" would be explaining the joke. Printing "noun." in italic underneath, the way a dictionary marks a part of speech, treats the missing word as if it already existed and had simply been defined at unusual length. It's a small, dry move, and it carries the whole argument without a single line of complaint anywhere on the shirt.
Which relationships actually earn this treatment?
The ones that take three steps or more to describe, and that plenty of people independently share.
"My brother's wife" is two steps, and English already has a word for her — sister-in-law — so printing the phrase there would just be a longer way of saying something the language already covers. It's a gap in the vocabulary rather than a gap in the family, which is a different problem from the one where a single birth renames five people in the same afternoon and the words simply haven't caught up yet. The format wants a relationship with no English shortcut at all, and one common enough that a stranger recognises it on sight rather than reading it as a private family riddle. It borrows the same trick as a single loaded word filling the whole chest, except here the syntax is left in rather than stripped out.
The test that actually decides it
Try saying the relationship out loud to a stranger. If you reach for a shortcut and there isn't one, if you end up narrating the whole chain every time, the way you would here, that's the sign this treatment is doing real work rather than manufacturing a gap that wasn't there.
Do other languages really have a single word for this?
Some do — a number of kinship systems around the world assign a dedicated term to relationships English only manages by chaining possessives together.
That's a genuine, well-documented fact about how languages divide up family, not a claim about any one language in particular. It's worth knowing mainly because it proves the English gap is a choice the language made rather than something relationships are inherently too complicated to name. This shirt isn't translating anybody else's word, though — it's pointing at the hole where English's own would go, which is a different design from setting the same idea in two languages side by side.
Do I need my mother-in-law's blessing before I print this?
Nobody's actual name appears on the shirt, but the relationship is specific enough that she'll know exactly who it means, so the honest answer is: ask her anyway.
There's no name to license and no owner of a relationship category — anybody can print "my brother's wife's mother" without clearing it with a dictionary. What matters is whether she'd find it funny or find it exposing, and a phrase this precise is really about a real person even without her name on it. Showing her the design before it ships is a better test than guessing.
Does the joke work for a shorter gap in the vocabulary too?
Yes, as long as English genuinely lacks a word for the shorter chain too, which rules out some of the obvious-seeming candidates.
A two-step relationship that already has a compact English term — sister-in-law, stepfather — loses the joke, because there's no gap left to expose. A three-step chain with no shortcut, a co-parent's parent, a spouse's ex's child, keeps the mechanism intact at a shorter length; it just crops the shirt with fewer words on it.
Does it print well?
Yes — dense serif type across three lines needs a garment wide enough to keep the smallest line legible.
Heavy black capitals hold their weight well in a single ink, and the italic "noun." underneath is small enough that it should sit in the same colour rather than a second one, or it competes with the headline for attention it doesn't need. Flat shapes with hard edges are what actually survive a weave, which serif capitals at this size already are. A wide chest keeps the top line from wrapping badly on the smaller sizes.
Dirty white, bone and pale grey all let black serif type read this cleanly.
How do I get one made?
Describe the relationship and how many steps it takes to say it at JustOG — the chain, the missing word, whoever it's for.
Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to order and shipped.
Designs other people have published are in the shop.
Nine words, three lines, and a relationship everybody has had to explain out loud at least once.