The story
From broad (describing a wide front flap) + fall (a historical tailoring term for a drop-front trouser flap that buttons at the waist).
Etymology from Wiktionary, CC BY-SA 4.0.
broadfall trousers
Today it means: A traditional style of men's pants defined by a wide, hip-to-hip front flap that buttons at the top and sides instead of using a standard zipper or modern fly. Full definition →