This study (a) examines the role of cognitive abilities, age and vocabulary in the development of definitions and (b) compares the development of definitions (in content and form) in children with and without Developmental Language Disorder (DLD). Definitions have been extensively studied in (non-)impaired populations. So far, no studies have tested the impact of cognitive abilities on the development of definitions. To address this gap, ten children with DLD and ten non-impaired peers were tested through a definition task and two cognitive tasks. The results exhibited that the control group produced more accurate definitions, albeit only in content, than the impaired group. Regressions showed that, in the impaired group, the younger the participants the better the scores. For the non-impaired group, age and verbal working memory found to predict the performance on definitions. Thus, we deduce that (a) the development of definitions is driven by different mechanisms in (non-)impaired children and (b) the role of early intervention seems to be important for atypical populations.