affiant
noun
af·fi·ant ə-ˈfī-ənt 
: one who swears to an affidavit
broadly : deponent
Example Sentences
Recent Examples on the Web The affiant is identified as a violent crimes detective with the Santa Fe County Sheriff's Department. 
NBC News, 17 Dec. 2021 Based on the information/observations set forth in paragraph 22 ad 24, affiant believes that the target may utilize said firearm against law enforcement during the execution of the warrant. Bruce Vielmetti, Milwaukee Journal Sentinel, 11 July 2019
NBC News, 17 Dec. 2021 Based on the information/observations set forth in paragraph 22 ad 24, affiant believes that the target may utilize said firearm against law enforcement during the execution of the warrant. Bruce Vielmetti, Milwaukee Journal Sentinel, 11 July 2019 Word History
Etymology
probably from affi(ance) entry 1 + -ant entry 1
First Known Use
1807, in the meaning defined above
Legal Definition
affiant
noun
af·fi·ant ə-ˈfī-ənt
: a person who swears to an affidavit compare deponent, witness