This study explored an alternative approach to assessing individuals’ word knowledge by gauging the ability to recognize subtle similarities and differences among associated terms. Informed by the theoretical and empirical work on relational reasoning, the Measure of Vocabulary Knowledge through Relational Reasoning (MVKR2) was developed and validated. Participants were 338 college students who completed the MVKR2, the Test of Relational Reasoning (TORR), and released items from the SAT Verbal and Math tests. The TORR and SAT tests were administered to examine the convergent and concurrent validities of the MVKR2. Findings from item confirmatory analyses and correlations demonstrated that the MVKR2 is a reliable and valid measure of vocabulary knowledge for college-age students. In addition, fluid relational reasoning ability was associated with the performance on this novel measure, but the association with vocabulary knowledge was stronger. When examined on the scale and item levels, the contribution of fluid relational reasoning varied across scales and items within each scale. This study offered an alternative way to examine vocabulary knowledge that has implications for future empirical research and instructional practice.