This lecture covers the study of word meanings, focusing on lexical semantics and its applications. It discusses word sense, lexemes, and semantic relations such as homonymy, polysemy, synonymy, hyponymy, hypernymy, and meronymy. The lecture also introduces WordNet as a resource for lexical semantics and explores how semantic relations are used to define word senses. Various applications of lexical semantics in language engineering, speech processing, spelling error correction, and information retrieval are presented.