Some authors have suggested that definitional skills include metalinguistic components (Watson, 1985; Snow, 1990; McGhee-Bidlack, 1991). The present study therefore empirically investigated relations between the ability to define words and level of metalinguistic awareness in 280 Italian children (with ages ranging from 5 to 11 years) and in two groups of 40 adults each (with low and high educational levels, respectively). We used a definitional task presenting 24 terms (nouns, verbs, and adjectives, which were either concrete or abstract) and a task examining 6 different aspects of metalinguistic awareness. Our aim was to demonstrate that metalinguistic skills can positively predict the formal quality of definitions and to identify various aspects of metalinguistic skills that might be directly related to definitional skills. Results showed better performance on both tasks as a function of age and educational level; they also confirmed the important roles of metalinguistic ability and educational level in producing well-structured formal definitions.