I've come across the word 머슴살이 and read in the dictionary that it means doing farm work. But looking around on the internet I'm not sure if there's some sort of historical meaning associated with the word. Perhaps it is / was used to refer to the work done by farmworkers / peasants / slaves in olden days. If so, or if it has a different origin, please let me know! I look forward to hearing your answers. :D
The term '머슴살이' can be separated into two parts :
'머슴' and '살이'
The word '머슴' refers to a person who worked for the rich '양반's and farm owners in order to earn money for their living. ('양반' refers to the people who are in class of wealth and power)
I said "who worked for the rich" because the word '머슴' was used in Chosun era. The important part is that although they did all the hard work, they weren't categorized as slaves.
They were just ordinary people who worked for the rich / farm owners in order to earn money.
So they were able to leave the work place if they wished, and were treated differently from actual slaves. Sometimes even those '양반's became one of '머슴's when they ran out of money or were kicked out of their family.
Today, the word '머슴' describes people who live similarly like those '머슴's from the past (with some 'slave' nuance included) : people who do all the hard work for employers in order to earn money. There is a high chance that work may include chores.
'--살이' is a suffix which means 'living -- life' but with negative nuance. For example, there are words such as :
= 시집 + 살이 = living daughter-in-law's life, doing all the chores for husband's family and getting scolded often
= 하루 + 살이 = living just for one day. Meaning that person has no plan for the future, or is doing something that might lead him/her to lose his/her life. (ephemera)
So when someone is doing '머슴살이', it means that person is doing chores and doing all the hard work for the employer(s) to earn their money. They most likely do not earn any respect from the employer(s) nor do they get the reputation for what they do.