Word learning is a complex activity whose mechanisms are not fully understood. For instance, there is an ongoing debate whether feedback is fundamental to learning the meaning of words. Three experiments and a simulation aimed to investigate the importance and role of feedback in learning a six-word vocabulary of an artificial language. In the experiments, participants had to guess what object in a visual array of objects was referred to by an utterance composed of unknown words. The words referred to objects characteristics like color, size or shape. Results showed that feedback led to a superior learning rate. However, some learning did occur without feedback. A simulation further illustrated possible mechanisms responsible for learning with and without feedback. These data are consistent with the idea that the mechanism by which feedback particularly helps learning consists of reducing the amount of ambiguity in the environment.