This paper investigates the effect of using L1 translations versus L2 definitions on the learning and testing of L2 vocabulary recognition knowledge. For this study, 48 Japanese L2 learners of English studied 200 lexical items from the academic word list (AWL) over a 10-week period. To support their learning, the participants were provided with the meaning of the target language. The language in which the meanings were presented was manipulated such that the learners received half of them in their L1 and half in their L2. Similarly, at pre- and post-test stages, the participants were tested on their receptive knowledge of the vocabulary equally in both languages. Through a factorial repeated measures analysis of variance, the results showed that the students' recognition of the L2 vocabulary was significantly higher when asked to match the target vocabulary to L1 translations than L2 definitions. Furthermore, there was a significant interaction between study language and testing language, such that when study and testing language matched, the participants scored significantly higher. However, overall, the language in which the target vocabulary was studied did not matter for test scores. The implications of these results for learning, teaching, and test taking are discussed.