merman: half man and half fish; lives in the sea
imaginary being: a creature of the imagination; a person that exists only in legends or myths or fiction
sacrament: a formal religious ceremony conferring a specific grace on those who receive it; the two Protestant ceremonies are baptism and the Lord's Supper; in the Roman Catholic Church and the Eastern Orthodox Church there are seven traditional rites accepted as instituted by Jesus: baptism and confirmation and Holy Eucharist and penance and holy orders and matrimony and extreme unction