{n. phr.}, {informal} An unsolved or nagging problem. * /"My math course is a real monkey on my back," Jack complained./ Compare: ALBATROSS AROUND ONE'S NECK, MILLSTONE AROUND ONE'S NECK.
MONKEY ON ONE'S BACK
Meaning of MONKEY ON ONE'S BACK in English
Dictionary of English idioms . Словарь английских идиом. 2012