. learners‟ vocabulary maintenance. She has been motivated to conduct an action research titled Activities to increase adult learners’ retention of vocabulary at Yen Bai Centre of Continuing Education . the wide range of meaning communication in an L2 just cannot happen in any meaningful way.” This claim indicates the great importance of vocabulary. If someone has adequate vocabulary, he or. say dense hair instead of thick hair. 1.1.3. The roles of vocabulary in Foreign Language Acquisition Vocabulary is central to language and is of great significance to language learners. It