Used to refer to the entirety of something, often in the phrase 合切袋 (がっさいぶくろ) meaning a bag containing all one's belongings. The standalone use is somewhat literary or old-fashioned.
合切袋一つで旅に出た。
He set off on a journey with just one bag containing all his belongings.
彼は財産を合切失った。
He lost his entire fortune.
Standard kanji spelling for this noun.
The exact derivation is uncertain. The kanji 合 (together) and 切 (cut/limit) may suggest 'all together' or 'the whole lot', but the word is not transparently derived from these meanings.