Young children can sometimes acquire new vocabulary words with only limited, indirect exposure (Carey & Bartlett, 1978). We propose that structural alignment processes lead to fluent detection of commonalities and differences that facilitate incidental word learning. To test this, we adapted the Carey and Bartlett paradigm, varying the alignability of the objects that 4-year-olds saw while hearing the novel word chromium. In Experiment 1, children in the High-Alignment condition were significantly better than those in the Low-Alignment condition at identifying chromium objects in a subsequent task. In Experiment 2, we ruled out an alternative account by equalizing the overall amount of information presented to the two groups. We also found that the advantage of high alignment persisted after two-to-four days. These results suggest that structural alignment is a mechanism by which children can learn word meanings even in incidental word learning situations.