Alone or unaccompanied; without family or companions. Often used for moving, transfer for work, or travel (e.g., 'to go alone').
単身で上京して一人暮らしを始めた。
I moved to Tokyo alone and started living by myself.
彼は単身赴任で月曜日から金曜日まで別の街にいる。
He is on a solo job transfer and stays in another city from Monday to Friday.
単身で海外旅行に行くのはいい経験になる。
Traveling abroad alone can be a good experience.