The importance of vocabulary knowledge is well-established in second language (L2) research. Many studies have investigated the prominence of this variable in L2 skills. One of the vocabulary classifications is the size dichotomy and depth of word knowledge, the significance of which has been probed in many studies. However, few studies have investigated the interaction among such reader variables and text variables in reading comprehension. Consequently, this review endeavored to reconnoiter the lexical cohesion effects on reading comprehension and the contribution of vocabulary size and depth to the text's comprehension with high and low lexical cohesion. As a result, 60 Iranian EFL learners participated in the Vocabulary Levels Test (VLT) and Word Associates Test (WAT), reading comprehension tests with low and high lexical cohesion. The paired samples t-test and multiple linear regression analyses indicated that the student's reading comprehension scores on the test with high lexical cohesion were higher than on the text with low lexical cohesion. Additionally, the depth of vocabulary knowledge was a dominant prognosticator of the participants' reading comprehension, especially the texts with high lexical cohesion, suggesting that the vocabulary depth elements and lexical cohesion are related to each other than helping the students with more word knowledge depth to use the linguistic clues provided in the texts with higher lexical cohesion. The results have implications for teachers, students, and materials developers as well as the test designers to focus more on the depth dimension of vocabulary knowledge.
