As a fascinating and colorful part of English language, idioms highly affect fluency, but they are quite difficult to teach and learn, and they have often been neglected particularly in ESL/EFL settings. Considering the large number of English idioms, corpus linguistics can be of great benefit in prioritizing materials in language classrooms based on the frequency information. Accordingly, the present corpus-based study aimed at identifying the most frequent idioms in English language by analyzing the data coming from the Corpus of Contemporary American English (COCA), composed of more than 520 million words. The study involved writing a special script using Hypertext Preprocessor (PHP) language which resulted in the development of five idiom lists, each containing 50 most frequently used idioms in each one of the five genres in COCA including academic, fiction, spoken, newspaper, and magazine along with their frequency of occurrences. Comparison was then made across the mentioned five genres. It was found that the spoken genre included more idioms whereas the academic genre was the least idiomatic. Furthermore, various levels of overlap was found among different genres. The least and the highest levels of overlap was found between the academic and fiction genres and between the magazine and newspaper genres respectively. The academic genre had more overlap with the newspaper and magazine genres. The findings can benefit EFL materials developers, teachers, and learners in recognizing and including frequently-used authentic idioms in language classrooms and textbooks.
