/playn"sawng', -song'/ , n.
1. the unisonous vocal music used in the Christian church from the earliest times.
2. modal liturgical music; Gregorian chant.
3. a cantus firmus or theme chosen for contrapuntal development.
4. any simple and unadorned melody or air.
Also, plain song . Also called plainchant (for defs. 1, 2).
[ 1505-15; trans. of ML cantus planus ]