Being a copy editor (grammar and spelling and clarity and chronology and fact-checking, etc.) and having been a legal assistant (details, details, details, plus grammar and spelling and clarity and chronology and fact-checking), I'm very sensitive to word choices and their exactness and fit within the context of phrases and sentences and overall story structure. And I can point to a reference book or two which backs me up.
First, I use "pantster" not "pantser" to describe us plot-challenged novelists. Say it out loud and you hear the second T. It is a word built like "teamster" or "gangster" or "youngster" with the "ster" suffix.
Second, I am an author, not a writer. It is a fine distinction but here is my argument for using same. I create, therefore I am an author (the "au" is a truncated prefix for "author" and/or "to hear/listen" and/or "self" which my mind combines to mean "self-generated words, spoken or written" and the "thor" meaning "God/Creator" further emphasizing the creation part).
The writers, I maintain, are directed to bring to life someone else's idea. Thus the term "screenwriter" is usually an independent freelancer who takes an author's book and adapts it into a screenplay for either a movie or a live theater production.
A copywriter is just that, someone who writes copy (think advertisements, whether for print or for radio/TV, etc.). That writing assignment, job if you will, is at the urging of the person who hired them.
A ghost writer is, again, one hired to do a task at the prompting of the employer, the author, who needs help with his vision, his idea, his plot, his story. I've never heard of a ghost author.
Web11 defines "author" as one who originates or creates. While I may write, I am not a writer. Not in the strictest sense of the word. Not that you can't be a writer AND an author. But there is a difference.