Formal:
* Neologist: This is the most direct and accurate term, derived from the word "neologism," meaning a newly coined word or expression.
* Lexicographer: While lexicographers primarily document existing words, some might also be involved in creating new words, especially for specialized fields.
* Linguist: Linguists study language in all its aspects, which can include the creation of new words.
Informal:
* Wordsmith: This term is often used for someone who is skilled with language, including creating new words.
* Inventor (of words): This is a simple and straightforward way to describe someone who creates new words.
* Word creator: Similar to "inventor," this highlights the act of creating new words.
The best term to use will depend on the specific situation and the desired level of formality.