Well-developed lexical representations are important for reading comprehension, but there have been no prior attempts to track growth in the depth of knowledge of particular words. This article examines increases in depth of vocabulary knowledge in 4-5-year-old preschool students (n = 240) who participated in a vocabulary intervention that taught words through book reading and book-related play. At pretest and posttest, students defined words verbally and by using gesture. Responses were coded for type of semantic information given. There were significant increases in depth of knowledge for all word types. Concrete nouns were learned significantly better than all other word types, and verbs were learned significantly better than abstract nouns and adjectives. Analysis of semantic content provided nuanced information about word learning across word types. Synonyms and contextual information were learned well for all word types, whereas functional information was learned best for concrete nouns. These results suggest that ease of word learning may not be influenced solely by perceptual accessibility of words but also by the kind of instructional information that can be provided for different word types.