Progress toward establishing a model of lexical development to guide vocabulary acquisition research requires more precise specification of the various dimensions of lexical competence, the interrelationships among them, and how they interface with processes of word learning and use. Three dimensions of lexical competence are proposed: (a) partial to precise knowledge, (b) depth of knowledge, and (c) receptive to productive use ability. The relationship between the two knowledge dimensions and the acquisition of word meaning is considered, with emphasis on the complexity of the semantization1 process and on the need for redefining lexical development as both item-learning and system-changing. The adequacy of the three-dimensional description as a reflection of the process of vocabulary development is then discussed. Consideration of the nature of the developmental interrelationships among the dimensions raises two further questions: (a) Is depth of knowledge a prerequisite for developing precise comprehension? and (b) Are precise knowledge and depth of knowledge prerequisites for a word to become productive?