This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. One who consistently denies, criticizes, or doubts; a detractor.

n. someone with an aggressively negative attitude

"Among this group, I am known as the naysayer — well that is the only one of the names they call me that I can repeat publicly."

yea-sayer   

resister    obstructionist    obstructer    obstructor    thwarter   

technophobe   

Breyer    Dreyer    Mayer    Sayer    Speyer    assayer    bayer    brayer    conveyer    conveyor