One who gives moral but not material support. The allusion is to boxing or prize-fighting, where each combatant has a bottle-holder to wipe offblood, refresh with water, and do other services to encourage his man to persevere and win.
“Lord Palmerston considered himself the bottle-holder of oppressed States… . He was the steadfast partisan of constitutional liberty in every part of the world.”—The Times.
· 
· 