expression, noun
wearing only a loincloth; nothing but a loincloth
Often used in the pattern 〜で, 〜の, or 〜になり to describe a state of undress where someone is wearing nothing except a traditional Japanese loincloth (fundoshi).
See also: パンツ一丁 · ふんどし一丁 (ふんどしいっちょう)
彼は褌一つで川に飛び込んだ。
He jumped into the river wearing nothing but a loincloth.
祭りでは、男たちが褌一つの姿で神輿を担ぐ。
At the festival, the men carry the portable shrine dressed only in loincloths.
Similar meaning but refers to modern underpants (パンツ) instead of a traditional loincloth (褌).
Synonymous variant using 一丁 (いっちょう) instead of 一つ (ひとつ); both mean 'only a loincloth'.
Compound of 褌 (fundoshi, 'loincloth') + 一つ (hitotsu, 'one'), literally 'one loincloth', implying nothing else is worn.