Formal terms:
* Sesquipedalian: This is the most common and accurate term. It literally means "a foot and a half long" and refers to using long words.
* Logophile: This term means "lover of words," and while it doesn't specifically refer to using big words, it can imply an overuse of complex vocabulary.
* Pedantic: This refers to someone who is overly concerned with minute details and rules, often displaying their knowledge in a showy way.
Informal terms:
* Show-off: This is a direct and somewhat negative way to describe someone who uses big words to impress others.
* Pretentious: This is a more nuanced term that implies the person is trying to appear more intelligent or sophisticated than they are.
* Wordsmith: This term is more neutral and can be used to describe someone who enjoys using language, but can also imply that they're more focused on the elegance of their language than the clarity of their message.
Ultimately, the best term to use will depend on the context and the specific way the person is using big words.