The length of words reflects their conceptual complexity.

Are the forms of words systematically related to their meaning? The arbitrariness of the sign has long been a foundational part of our understanding of human language. Theories of communication predict a relationship between length and meaning, however: Longer descriptions should be more conceptually complex. Here we show that both the lexicons of human languages and individual speakers encode the relationship between linguistic and conceptual complexity. Experimentally, participants mapped longer words to more complex objects in comprehension and production tasks and across a range of stimuli. Explicit judgments of conceptual complexity were also highly correlated with implicit measures of study time in a memory task, suggesting that complexity is directly related to basic cognitive processes. Observationally, judgments of conceptual complexity for a sample of real words correlate highly with their length across 80 languages, even controlling for frequency, familiarity, imageability, and concreteness. While word lengths are systematically related to usage-both frequency and contextual predictability-our results reveal a systematic relationship with meaning as well. They point to a general regularity in the design of lexicons and suggest that pragmatic pressures may influence the structure of the lexicon.