From kvetch + -er, or Yiddish קוועטשער (kvetsher).
kvetcher (plural kvetchers)
- A person who kvetches; a complainer, kvetch.
2017, Gregg Hurwitz, The Nowhere Man:
My Herb, may he rest in peace, worked his fingers to the bone and never complained a day in his life. We knew what hardship was, our generation... We weren’t kvetchers.