Something that is lexical is related to words. A dictionary is lexical, as is a tongue-twister!
Lexicon is a fancy word for a dictionary. The word lexical is an adjective that describes anything that pertains to words or vocabulary, or to even language more generally. Solving a crossword puzzle is a lexical activity. A linguist, or someone who studies words for a living, has a lexical job. If you find yourself frequently correcting people when they misuse words, then it's likely you have a love of all things lexical.