This study aims to investigate the effects that the L1 and L2 definitions and semantic features of words have on vocabulary learning. For this purpose, sixty-seven students were divided into the bilingual and monolingual definition groups. The bilingual group performed significantly better on the immediate post-test but not on the delayed test. The results suggest that the bilingual definitions are more effective for the initial learning of words but, the monolingual definitions could be more effective for retention. Regarding the effect of semantic features, the participants scored significantly higher for concrete nouns than for abstract nouns on both post-tests, suggesting that concrete nouns are easier to learn. Lastly, the bilingual group performed better for concrete nouns on the immediate post-test. No difference existed on the delayed test. Implications of the findings are discussed.