In upper elementary grades, once word recognition is efficient, reading comprehension is more affected by processes such as vocabulary and background knowledge. One facet of vocabulary knowledge that is closely related to comprehension is the quality of formal definitions, as this knowledge reflects the student's awareness of decontextualized language. Spanish-English fourth-grade students who have just been transitioned to all-English classrooms gave definitions to words from Spanish and English expository passages before reading the texts and answering questions about them. The quality of formal definitions was correlated across the two languages, indicating cross-language transfer of this metalinguistic awareness. In addition, formal definition quality was related to reading comprehension both within and across languages.