There is strong agreement in the literature that the first language (L1) supports second language (L2) vocabulary learning particularly at early stages of learning. The present study examines the influence of word type on the use of L1 language to support L2 vocabulary learning. To this end, 130 Arabic-speaking tertiary elementary female learners of English were taught 24 unfamiliar English words in 4 sessions over 4 weeks. The participants were divided into three groups; (1) a group where target words were taught with the use of translation equivalents, (2) a group taught with L2-only-definitions and (3) a control group who received no special treatment. Comparing the participants' performance in pre-, immediate post-and delayed post-tests showed that the two experimental groups outperformed the control group, reflecting the benefit of the treatment. The results also showed greater vocabulary gains in terms of long-term retrieval for L1 use, but did not show consistent patterns for the special benefit of L1 in terms of specific word types. The results are interpreted in light of the existing literature and relevant bilingual lexicon models. Pedagogical implications and suggested research directions are also proposed.