"Collaborative inhibition" is the counterintuitive finding that learners working in a group recall less information compared with the combined nonredundant output of the same number of learners working individually (Weldon & Bellinger, 1997). Although research has shown that collaborative inhibition occurs for a variety of to-be-learned material, no research has evaluated whether the effect emerges for key-term definitions. In two experiments, learners individually studied key-term definitions during an initial study phase. Learners then completed a retrieval practice phase, which occurred either collaboratively or individually. After a delay, all learners individually completed a final test phase. Performance during the retrieval practice phase is of greatest interest for present purposes. Results established collaborative inhibition such that recall was lower for learners in the collaborative group versus the individual group, which provides novel evidence to the collaborative memory literature by demonstrating that the effect emerges with key-term definitions.