The fundamental knowledge base of effective vocabulary teaching and learning includes the extensive body of research on vocabulary instruction methods and the process of language acquisition. This knowledge base also includes the current understanding of issues and constraints of literacy instruction in language classrooms (Arnott & Mady, 2013). Research in the past has increased the depth of understanding issues related to vocabulary, including the nature of word knowledge, pedagogy for developing vocabulary acquisition, and the complex issues between vocabulary and comprehension (Fernandes, Querido, Verhaeghe, Marques, & Araújo, 2017).Research has also shed light upon effective instructional practices for teaching vocabulary. In older studies such as Krashen (1985) and Ellis (1994), Krashen claimed that "conscious learning" does not make any major contribution to competence and did not devalue direct teaching through involving learners in non-anxiety-provoking communication activities. On the other hand, Ellis (1994) reviewed