UNDEREXTENSION By N., Pam M.S. - April 29, 2013 noun. the inaccurate limitation of the utilization of a term or word, which is a mistake typically made by young kids leaning language. UNDEREXTENSION: "You'll need to address underextension at least once in your papers." Related Psychology Terms OVEREXTENSION PARAPHASIA PARATAXIS UTTERANCE ISOLATING LANGUAGE TELEGRAPHIC SPEECH ORALISM PRONOUN ANAPHORA PIVOT GRAMMAR Cite this page: N., Pam M.S., "UNDEREXTENSION," in PsychologyDictionary.org, April 29, 2013, https://psychologydictionary.org/underextension/ (accessed September 5, 2019).