gainsayer
One who contradicts or denies what is alleged; an opposer.
A person who gainsays others; a disagreeable person.
First, The writer, positively asserts, "That Wood's halfpence were current among us for several months with the universal approbation of all people, without one single gainsayer".
Where it comes from
From Middle English aȝenseyere, equivalent to gainsay + -er.
Adapted from the Wiktionary entry gainsayer (CC BY-SA 4.0).