An oath-taker is someone who swears, vows, or avows something. A swearer is someone who makes a solemn promise or declaration, usually with an appeal to a higher power, while a vower is someone who makes a promise or vow, and an avower is someone who declares or affirms something. All of these terms refer to someone who takes an oath, which is a solemn promise or declaration made with an appeal to a higher power.