Picture the scene: a family gathering, full of warm chatter and shared food. But in the corner, a palpable tension. You need to ask someone to pass the salt, but that someone is your mother-in-law. You catch her eye, offer a slightly pained smile, and perform an elaborate pantomime of a salt shaker. The awkwardness is thick enough to cut with a knife.

For many of us, navigating in-law relationships involves a delicate dance of politeness and careful topic selection. But what if this social dance was codified into the very language you speak? What if, to show respect, you were forbidden from speaking directly to your mother-in-law and had to use an entirely different set of words whenever she was nearby? This isn’t a hypothetical scenario. It’s a real and fascinating sociolinguistic phenomenon known as an “avoidance register,” or an “in-law language.”

What on Earth is an Avoidance Register?

In linguistics, a register is a variety of language used for a particular purpose or in a particular social setting. We all use them. The way you speak to your boss is a different register from how you speak to your best friend, which is different again from how you speak to a toddler. We switch our vocabulary, tone, and even sentence structure without a second thought.

An avoidance register is a highly specialized and formalized version of this. It’s a complete system of speech reserved for situations involving specific kin who are considered “taboo.” Speaking to them directly, or even using everyday language in their presence, is seen as deeply disrespectful. These registers are not just about being polite; they are intricate linguistic systems designed to maintain social distance and harmony.

While this practice has been documented in various parts of the world, including among some Bantu-speaking peoples in Southern Africa (known as Hlonipha), the most extraordinary and well-documented example comes from the rainforests of North Queensland, Australia.

The Dyirbal People and the ‘Mother-in-Law Tongue’

The Dyirbal are an Aboriginal Australian people whose traditional lands are in North Queensland. At the heart of their culture is a complex kinship system with strict rules governing social interaction. One of the strongest taboos was between a man and his mother-in-law. They were forbidden from making eye contact, touching, or speaking directly to one another.

So, how did they communicate when they were in the same camp or family group? They used language. But not their everyday language. They used an entirely separate, parallel language.

The Dyirbal people essentially had two languages that every member of the community had to learn:

• Guwal: The “everyday” language, used in most daily situations with non-taboo relatives and friends.
• Dyalŋuy (or Jalnguy): The “avoidance language” or, as it’s famously known, the “mother-in-law language.”

What makes this system so remarkable is how these two languages relate to each other. According to the foundational work by linguist R.M.W. Dixon, Guwal and Dyalŋuy shared the exact same phonology (sound system) and grammar (rules for sentence structure). If you knew how to form a sentence in Guwal, you knew how to form one in Dyalŋuy. The difference was one thing, and one thing only: the vocabulary.

A Tale of Two Vocabularies

The lexicon—the words for things, actions, and concepts—was almost entirely different between the two registers. To switch from everyday talk to avoidance talk, a speaker had to swap out nearly every single word.

Consider these examples:

One fascinating aspect of the Dyalŋuy vocabulary is that it’s more generic than the everyday Guwal. For example, where Guwal might have dozens of specific words for different species of lizard or bird, Dyalŋuy might only have one or two general terms like “lizard” or “bird.” This makes sense. In a taboo situation, the goal is not detailed, elaborate conversation but essential communication. You need to convey meaning clearly without violating social boundaries.

How Did It Work in Practice?

The use of Dyalŋuy was a masterful piece of social choreography. A man wouldn’t speak Dyalŋuy *to* his mother-in-law. Instead, he would use it to speak to his wife, his child, or anyone else in the group while his mother-in-law was within earshot. She, in turn, would do the same. This allowed vital information to be shared across the group without anyone breaking the powerful social taboo.

In fact, out of respect, anyone in the presence of the two taboo relatives might switch to Dyalŋuy. This meant that from a young age, children grew up hearing and learning both vocabularies simultaneously. Being fluent in Dyirbal meant being fluent in both its everyday and its avoidance forms. It wasn’t an optional extra; it was a fundamental part of being a competent member of the community.

The Social Fabric of Language

The Dyirbal mother-in-law language is a profound illustration of a deeper truth: language is not merely a tool for exchanging data. It is the very fabric of our social lives. It encodes our values, reinforces our social structures, and provides the tools we need to navigate complex human relationships.

These avoidance registers show the incredible creativity and adaptability of the human mind. Faced with a strict social requirement—the need to show immense respect by maintaining distance—a culture didn’t just fall silent. It developed a parallel linguistic universe, a complete and functional language existing solely to manage that one social rule.

Sadly, the Dyirbal language is now critically endangered, and the use of the Dyalŋuy register has all but vanished. Its loss is not just the loss of words, but the loss of a unique cultural system for managing kinship and respect—a system woven directly into the grammar and vocabulary of a community.

The next time you find yourself struggling for the right words around a relative, take a moment to appreciate the hidden social work your language is doing for you. While we may not have a full-blown “in-law tongue,” the subtle shifts in our tone, our choice of title, and the topics we avoid are all echoes of the same phenomenon: language as the ultimate guide to the intricate map of human society.