Acquiring the meaning of a new word in a foreign language can be achieved either by rote memorizing or, similar to meaning acquisition during infancy, by extracting it from context. Little is known about the brain mechanisms involved in word learning. Here we demonstrate, using event-related brain potentials, the rapid development of a brain signature related to lexical and semantic processing during contextual word learning. Healthy volunteers engaged in a simple word-learning task were required to discover the meaning of a novel word from a context during silent reading. After 3 exposures, brain potentials to novel words in meaningful contexts were indistinguishable from real words, although this acquisitioneffect was not observed for novel words, for which sentence contexts allowed no meaning derivation. Furthermore, when the learned novel words were presented in isolation, an activation of their corresponding meaning was observed, although this process was slower than for real words.