noun
officiant; presider
Formal term for the person who conducts or presides over a ceremony, especially weddings or religious rites.
結婚式の司式者は新郎新婦の友人だった。
The officiant at the wedding was a friend of the bride and groom.
教会の司式者が式を執り行った。
The church officiant conducted the ceremony.
Compound of 司 (preside over), 式 (ceremony), and 者 (person). The exact historical derivation is uncertain, but the spelling is conventionally associated with the meaning.