돌싱(Dolsing) is from 돌아온 싱글. 돌아온(Doraon) means 'having come back.' 싱글(Singguel) is Korean pronunciation for English, single. So basically, it means 'came back to single.'
Check the pronunciation.
Another popular one that are being used a lot since recently is 모태솔로(Motaesolo).
Do you know the movie, the 40 year old virgin?
He has never did 'it' with a woman and never really had a girlfriend. We can call him 모태솔로.
모태(Motae) means Mom's womb. 솔로(Solo) is from English word, Solo.
You might be able to guess what it means. Yes!! Solo from the womb of Mom.
If someone is 모태솔로, that person never had a girlfriend or boyfriend.There was even a TV program which gathered 모태솔로 people and set up blind dates for them. lol.