Lexicon/ˈleksɪkɑːn/ Definition 1 of 3Pro Tip 1/3Word Reference Use 'lexicon' when referring to a source you look in for word meanings. I couldn't remember the word, so I checked the lexicon. Pro Tip 2/3Academic Projects In school assignments, mentioning a 'lexicon' shows extensive research of terms. My thesis included a lexicon of ancient Greek terms. Pro Tip 3/3Not Casual 'Lexicon' is formal; use simpler words like 'list' in everyday conversation. For class, consult the lexicon; at home, just use a word list.