store of patience; one's patience
Figurative noun for the capacity to endure or tolerate. Almost exclusively used in the set phrase 堪忍袋の緒が切れる (one's patience runs out / one's temper snaps).
See also: 堪忍袋の緒が切れる
His rude attitude finally made me snap.
Even someone that patient can reach the end of their tether.