stark-naked; completely naked
Literary or emphatic expression meaning 'without a single thread on one's body'. Often used in descriptive or dramatic contexts.
See also: 一糸まとわぬ (いっしまとわぬ)
He jumped into the lake stark-naked.
They were photographed completely naked.
素っ裸 is a colloquial, somewhat rough way to say 'stark-naked'. 一糸まとわず is more formal and literary.
Standard kanji spelling; まとわず is often written in kana.
Alternate kanji spelling using 纏; less common but still seen.
From 一糸 (one thread) + まとわず (negative of まとう, to wear), literally 'not wearing a single thread'. The exact origin is uncertain, but it is a set phrase emphasizing complete nudity.