Possible Clues:

• (Ritual) incantation
• Church worker's song
• Emulate a hazan
• Type of group singing
• Your pen might give this an inclination to be musical
• Canticle
• How 12 across might have a leaning to follow 15 across to be a sort of 4 across, perhaps
• Rhythmic shout
• Medieval rap
• Sing a simple song