Lexical means relating to words and vocabulary. When linguists study the lexical differences between British and American English, they're comparing the actual words each culture uses: “lift” versus “elevator,” “biscuit” versus “cookie,” “boot” versus “trunk.”

A dictionary is sometimes called a lexicon, which is a collection of all the words in a language or field of study. Medical students must master an enormous lexical challenge, learning thousands of specialized terms like “myocardial infarction” (heart attack) and “dysphagia” (difficulty swallowing). Scientists working in different fields can struggle to communicate because each has its own lexical territory.

When teachers talk about building your lexical knowledge, they mean expanding your vocabulary and understanding more words. Lexical is the adjective form of lexicon, so anything lexical deals with words themselves rather than how we arrange them in sentences (that's grammar) or how we pronounce them (that's phonetics). A lexicographer is someone who writes dictionaries, spending their days thinking about what words mean and how to explain them clearly.