Initial vocabulary acquisition is established through mapping second language (L2) word form to the existing first language (L1) meaning. However, although raised by some research, the effect of word translation equivalence on L2 vocabulary uptake is downplayed or disregarded. This study investigates the relationship between L1 lexical translation equivalence and L2 vocabulary acquisition in an experimental setting. A total of 156 native Arabic participants were given a vocabulary test in which they had to identify whether a word was known to them and then to supply the meaning of the word in their L1 and/or L2. The findings showed that L2 words with direct Arabic translation equivalents were significantly learned than words which do not. The study also indicated a smaller word frequency effect on learning words with non-direct L1 translation equivalents.