en گفتار درمانی Speech therapy پژوهشي Original Research Articles <strong>Objectives</strong>: Word definition skill is a complex language ability in which meta-linguistic awareness and literacy skills play a critical role. The present study examined the development of word definition skills in Persian-speaking children aged 4.5 to 7.5 years, concerning content and form aspects.<br> <strong>Methods</strong>: This was a cross-sectional and analytic-descriptive study. The study subjects were 107 children of three age groups, as follows: 54-65-month-olds, 66-77-month-olds, and 78-90-month-olds. The study participants were selected from kindergartens and schools in districts 1, 7, and 17 of Tehran City, Iran, by multi-stage sampling method. In the word definition task, children were requested to define the words. To analyze the obtained data, the Kruskal-Wallis test was used.<br> <strong>Results</strong>: The obtained results indicated that the mean score of content (P=0.001) and form (P=0.002) aspects of word definition significantly increased with age in the study participants.<br> <strong>Discussion</strong>: A shift from functional and objective responses towards meta-linguistic definitions, i.e. further developed in terms of content and form, was observed with aging. At the age of 7 years, definitions reflect the hierarchical nature of nouns, and applying the class name begins at this age. The age of reaching a specific class seems to be affected by the lexical category.<br> <gdiv></gdiv> Development, Word definition, Child, Semantic 419 430 http://irj.uswr.ac.ir/browse.php?a_code=A-10-970-1&slc_lang=en&sid=1 Maryam Malekian m.malekian6789@yahoo.com 0000-0001-5060-8792 No Department of Speech Therapy, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran. Talieh Zarifian t.zarifian@yahoo.com 0000-0002-6067-829x Yes Department of Speech Therapy, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran. Robab Teymouri robab.teymouri@yahoo.com 0000-0002-5954-231x No Pediatric Neurorehabilitation Research Center, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran.