Readers accurately monitor their incidental word learning success during silent reading

College-age adults who are skilled at reading use sentence context and morphemic information to learn definitions for new words they encounter in print (e.g., Tong et al., 2014). Often, the definitions that adult readers are learning are for word forms that already exist in their mental lexicon (Hulme et al., 2019). Readers demonstrate discrepancies between confidence in what they are retaining during reading and what they actually recall after reading (e.g., Sperling et al., 2004). Thus, metacognitive awareness is undoubtedly important for vocabulary learning. Few studies have investigated the role of metacognition in adults' word learning during reading. In the current study, we examined readers' metacognitive awareness and learning for novel compound pseudowords. Participants read sentences containing semantically opaque or transparent novel compound words in informative sentence contexts. Reading times were recorded, and readers judged how well they derived and would remember the novel words' correct definitions. After reading, participants took a surprise vocabulary test. Sentences containing opaque novel compounds were difficult, indicated by longer reading times. Participants were also less confident in their abilities deriving definitions for opaque than transparent words, and were less accurate on the vocabulary test for opaque words. Participants judged making an inference to define opaque compounds as more difficult than for transparent compounds, suggesting awareness of word learning difficulty. Overall, metacognitive judgments were mostly accurate. However, individual readers' accuracy varied greatly. These results provide a start to understanding how incidental vocabulary learning, and monitoring for this, proceeds in skilled (college-level) adults.