Without backing, in a way: Var

• Like many doo-wop sessions (var.)
• Like many "Glee" numbers: Var
• Without any musical accompaniment (var.)
• Like some choirs: Var.
• Like many doo-wop groups: Var

Wiktionary Word definitions in Wiktionary
adv. (alternative spelling of a cappella English)

Wikipedia Word definitions in Wikipedia
Acapella is an historic trimaran sailboat , designed and built by Walter Greene in 1978 and later renamed Olympus Photo . Walter and his wife Joan raced in the 1978 Round Britain race, coming in 1st in class and 4th overall. Later that year, Canadian Mike ...