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Longman Dictionary of Contemporary English
one-man band
noun
EXAMPLES FROM OTHER ENTRIES
▪ It's a small local radio station, really just a one-man band.
EXAMPLES FROM CORPUS
▪ An impressive variety of practices is featured in the exhibition, from the one-man band to the big, quoted companies.
▪ But as a one-man band, his overheads were similarly negligible.
▪ Can a journalist ferret out the facts while operating as a one-man band?
▪ Lunchtime on a day in June, cadenza in the rising wind: is there anything wrong with a one-man band?
Wiktionary
one-man band

n. 1 A musician who plays several musical instruments at once. 2 (context idiomatic by extension English) An organisation or business that is effectively run by only one person.

Wikipedia
One-man band

A one-man band or one-woman band is a musician who plays a number of instruments simultaneously using their hands, feet, limbs, and various mechanical and/or electronic contraptions. One person band musicians also often sing while they perform. The simplest type of "one-person band" — a singer accompanying herself on acoustic guitar and playing a harmonica mounted in a metal "harp rack" below the mouth — is often used by buskers and folk music singer-guitarists. More complicated setups may include wind instruments strapped around the neck, a large bass drum mounted on the musician's back with a beater which is connected to a foot pedal, cymbals strapped between the knees or triggered by a pedal mechanism, tambourines and maracas tied to the limbs, and a stringed instrument strapped over the shoulders (e.g., a banjo, ukulele or guitar). Since the development of Musical Instrument Digital Interface (MIDI) in the 1980s, musicians have also incorporated chest-mounted MIDI drum pads, foot-mounted electronic drum triggers, and electronic pedal keyboards into their set-ups.