Rare Christian term for a priest who hears confessions. In modern Japanese, 聴罪司祭 (ちょうざいしさい) is more common.
A confessor has the role of hearing believers' confessions.
Compound of 告解 (こっかい, 'confession') and 師 (し, 'master' or 'specialist'). The exact historical derivation is uncertain; the spelling is conventionally associated with the Christian meaning.