Answer: acapella

AnswerCrossword Clue
ACAPELLA

Without instrumental accompaniment (var.)

ACAPELLA

Without instrumentation

ACAPELLA

Without any musical accompaniment (var.)

ACAPELLA
Like many doo-wop sessions (var.)
ACAPELLA
Like some choirs: Var.
ACAPELLALike many doo-wop groups: Var.
ACAPELLALike many "Glee" numbers: Var.