single man; bachelor
Refers to an unmarried man, often with a nuance of being available or living alone. Common in everyday conversation and writing.
He is still a single man.
Life as a bachelor is carefree.
Compound of 独身 (どくしん, 'unmarried') and 男 (おとこ, 'man'). The exact historical derivation is straightforward; the word is a transparent modern compound.