The psalm usually appointed for penitential acts, being the 50th psalm in the Latin version. It commences with the word miserere.

A musical composition adapted to the 50th psalm.

Miserere by Gregorio Allegri is a piece of a cappella religious music (a setting of Psalm 50/51) composed during the reign of Pope Urban VIII, probably during the 1630s, for use in the Sistine Chapel during matins on Wednesday and Friday of Holy Week. It was the last of twelve falsobordone Miserere settings composed and chanted at the service since 1514 and the most popular: at some point, it became forbidden to transcribe the music and it was only allowed to be performed at those particular services, adding to the mystery surrounding it. Writing it down or performing it elsewhere would be punished by excommunication.

A small projecting boss or bracket, on the under side of the hinged seat of a church stall (see Stall). It was intended, the seat being turned up, to give some support to a worshiper when standing. Called also misericordia.

the projecting bracket on the under side of the seats of stalls in churches.

Same as Ileus.