A Study of the Students’ Ability in Mastering Vocabulary Through Definition of the Words to the Eleventh Grade Students of MAN 1 Langsa

This research is a classroom action research. The aim of this research is to know the process of improving students’ vocabulary mastery by using the definition of the words for eleventh grade students of MAN 1 Langsa in the academic year 2018/2019. The method used in this research was classroom action research. The writer conducted this research from 8 February until 19 Ferbuary 2019 in MAN 1 Langsa. The subject was the students of XI IPA 1 in 2018/2019 academic year. This class consists of 16 students. In collecting the data, the writer used observation sheet and test. The test were given in pre-test, test 1 and test 2. The writer analyzed the mean score of each test to find out the improvement of students’ vocabulary mastery after the action was conducted and analyzed the percentage of students passed and failed in each cycle. The writer conducted the action the students’ vocabulary mastery increased optimally. It could be seen from the mean score of pre test is 57.8, post test 1 is 72.5 and post test 2 is 84.68. In the first test (pre-test) the students who passed the KKM were 4 students or 25%. In the second test (post-test 1) the students who the passed KKM were 10 students or 62.5%. In the third test (post-test 2) the students passed were 14 students or 87.5%. After applying the action the writer was able to solve the problem in improving vocabulary mastery. The students were able to imagine the word meaning By using the definition of the words in teaching vocabulary, students could easly understand and memorize new vocabulary. In the teaching process, when the writer uses the definition of the words, the students are enthusiastic and enjoy during teaching learning process.