The paper offers a rigorous characterization of the notion of lexicographic definition: a minimal paraphrase formulated in the same language as the word defined and satisfying six lexicographic principles, which are formulated and discussed. The major types of semantic components in a lexicographic definition are identified and described: firstly, central vs. peripheral components, semantic-class marking components, presuppositional components, actant-specification components, weak components, and metaphor-marking components; secondly, conjunctive and disjunctive components. Three additional topics are introduced: the roles that the definition plays in a lexical entry (accounting for the semantic, syntactic and lexically restricted cooccurrence of the headword); lexical units whose definition is problematic; lexical connotations and semantic labels. Though the perspective offered on lexicographic definition is theory-oriented-within the framework of Explanatory Combinatorial Lexicology (ECL)-, a strong emphasis is put on the writing of actual definitions, a couple dozen of which is proposed and analyzed.