Nature Human Behaviour, Published online: 15 June 2026; doi:10.1038/s41562-026-02493-6 Languages often co-express related meanings, either reusing words or combining parts of words. It is poorly understood when each strategy is favoured. Across 1,982 languages, Brochhagen et al. find the ease of disambiguation of co-expressed meanings to predict the strategy used, which suggests that co-expression strategies are adaptive to communicative efficiency.