Choosing which words to teach is a key consideration for language teachers and materials writers. Some studies have shown that teaching words in semantically related clusters can make learning more difficult. However, others argue it is the physical similarity of the referents of words that causes confusion. Importantly, studies have employed different methodologies, which may have contributed to the contradictory results. The present study addressed this contradiction by examining the target words from with the methodology of to determine the extent to which semantic relatedness and physical relatedness contribute to the learning burden of L2 vocabulary. Results showed that (1) semantic and physical conditions increased burden relative to an unrelated condition, (2) the greatest burden was found when words were both semantically and physical related, and (3) there was no difference in burden between semantically and physically related words. Pedagogical implications are discussed.