Vocabulary plays a central role in English language learning because without sufficient vocabulary L2 learners are not able to understand others or express their own ideas. Wilkins (1972) wrote that “. . . while without grammar very little can be conveyed, without vocabulary nothing can be conveyed” (pp. 111–112). This is a fact which is absolutely obvious in L2 learners’ experience with different languages, even without grammar, with some useful words and expressions, one can often manage to communicate. Lewis (1993) went further to argue, “Lexis is the core or heart of language” (p. 89). Particularly as students develop greater fluency and expression in English, it is significant for them to acquire more productive vocabulary knowledge and to develop their own personal vocabulary learning strategies. The prominent role of vocabulary knowledge in second or foreign language learning has been recently recognized by theorists and researchers in the field. Accordingly, numerous types of approaches, techniques, exercises and practice have been introduced into the field to teach vocabulary (Hatch & Brown, 1995). It is believed that communication could not be successful when individuals do not make appropriate use of correct and right words (Allen, 1983). Therefore, lexical knowledge plays an important role in learning English; L2 learners are required to learn words and use them properly so that they could be involved in effective communication. This is why Ellis (1990,