This study investigated the noun definitions given by Cantonese speakers at different ages. Definitional responses on six concrete nouns from 1075 children aged 4;10 to 12;01 and 15 adults were analyzed with reference to the semantic content and the syntactic form. Results showed that conventional definitions produced by Cantonese adult speakers were realized with specific superordinates and more perceptual than functional attributes. The content was carried by a syntactic frame, "NP[subscript 1] "is" NP[subscript 2]", where relative clause was not the predominant form of NP[subscript 2] as in the English definition forms. Core attributes signifying the defining properties increased significantly with age while non-core attributes were observed relatively evenly throughout all groups. Preschoolers tended to drop the sentential-subject (i.e., NP[subscript 1]) and the copula is, and produce more functional than perceptual attributes. By Primary-2 (P2) (about 7;0), the taxonomic relation was coded with the frame of "NP[subscript 1] "is" NP[subscript 2]". Beginning at P4 (about 9;0), children included a superordinate but the specificity of the adult-like superordinate was not achieved even by P6 (about 11;0). In general, developmental trends accorded with the trends observed in other languages, but typological features played a role in framing the development of the syntactic form. (Contains 3 tables and 2 figures.)