Morphological analysis and incidental learning are two vocabulary learning strategies that language learners may use in order to acquire the meanings of new words. To date, however, few studies have compared the effectiveness of these two strategies. Hence, the current study was carried out to compare the effect of morphological analysis and incidental learning of words that appeared in ten actual TOEFL reading passages from 2010 to 2018 (henceforth, TOEFL vocabulary/words). Eighty upper-intermediate Iranian foreign language learners participated in the study. A pretest was administered to determine the TOEFL words the participants could not supply a synonym, a similar expression, or a translation for at the onset of the study. Next, the participants were randomly divided into two groups: the Morphological Analysis (MA) group, who learned the vocabulary through learning the meanings of Greco-Latin roots in the words, and the Incidental Learning (IL) group, who learned the TOEFL vocabulary through multiple exposures to the words in different contexts. Then, a posttest was administered to investigate the effect of each of these strategies on recognizing the meanings of the TOEFL words. Running a t-test, the groups' mean scores on the pretest and posttest were compared. The results of the study indicated that the MA had a more significant effect on vocabulary retention than the IL. Based on the findings of the study, it is recommended that MA be employed as a valuable source for TOEFL vocabulary learning and teaching by both teachers and learners, and as a strategy for vocabulary teaching in ESP or EAP courses as the vocabulary in such courses is heavily loaded with Greek and Latin roots.
