English and Content Learning (ECI) has long been the study of elementary English education. It has recently emerged due to the introduction of English immersion. In the past ECI learning experiences, teachers in practice demanded for the provision of an ECI dictionary to support ECI teaching and learning in elementary school settings. This study is an important step towards responding to the need for developing a supporting dictionary for ECI classes. The ECI dictionary development was based on elementary school textbooks with focuses on social studies, math and science. The total number of 1,719 cognitive academic word entries was selected based on a frequency list and expert knowledge. The micro-structure of these entries was piloted and revised reflecting feedback received from teachers with two different approaches to teaching vocabulary. Final structure of cognitive academic entries includes form, structure, content and learning box. The outcome was an extracted list of head words and the dictionary information according to the micro-structure of form, structure, content and learning box. The ECI dictionary will provide teachers who are using any form of ECI with a referential support for target word information, usage and use, learning materials.