Adults often learn new meanings for familiar words, and in doing so they must integrate information about the newly-acquired meanings with existing knowledge about the prior meanings of the words in their mental lexicon. Numerous studies have confirmed the importance of sleep for learning novel word forms (e.g., “cathedruke”) either with or without associated meanings. By teaching participants new meanings for familiar word forms, this is the first study to focus exclusively on the specific role of sleep on learning word meanings. In two experiments participants were trained on new meanings for familiar words through a naturalistic story reading paradigm to minimize explicit learning strategies. Experiment 1 confirmed the benefit of sleep for recall and recognition of word meanings, with better retention after 12 hours including overnight sleep than 12 hours awake. Experiment 2, which was preregistered, further explored this sleep benefit. Recall performance was best in the condition in which participants slept immediately after exposure and were tested soon after they woke up, compared with three conditions which all included an extended period of wake during which they would encounter their normal language environment. The results are consistent with the view that, at least under these learning conditions, a benefit of sleep arises due to passive protection from linguistic interference while asleep, rather than being due to active consolidation.