1. A way of communicating that is shared between and understood by only a few people. My sister and I have had our own private language ever since we were girls—our brothers still can't understand it! After working together for so many years, Ellen and I have a private language that is all our own.

2. philosophy A type of inner language only comprehensible to a single person. The concept was introduced by Ludwig Wittgenstein, who argued that it could not exist. The concept of private language is still a topic of debate among philosophers, especially due to its potential ramifications for metaphysics.