To cause liquid to stop flowing or to remove flowing water from something.
From de- (remove) + flow (movement of liquid). Flow comes from Old English flowan, a Germanic root meaning 'to move in a stream,' combined with the Latin prefix de- meaning away or down.
The de- prefix is incredibly productive in English, and deflow is one of those rarely-used words that shows how the same building blocks create hundreds of different technical meanings in specialized fields like drainage and hydraulics.
Complete word intelligence in one call. Free tier — 50 lookups/day.