quartet

noun

1. A group of four people or things, particularly

   “The last of the quartet of American fighter pilots to join the RAF before the war was Cyril 'Pussy' Palmer, who was born in Cleveland, Ohio, in March 1918.”

2. A group of four people or things, particularly

   “The string quartet played some chamber music.”

3. A group of four people or things, particularly

   “He composed a string quartet.”

4. A group of four people or things, particularly

   “The barbershop quartet performed the composition a cappella.”