Definitions

1. noun

A pointed or jagged rock or boulder, typically found in a river or stream.

“The hikers had to navigate around the large seif in the river to avoid getting injured.”

2. noun

A sharp or projecting rock in a river, used in whitewater rafting or kayaking to gain speed or make a turn.

“The experienced kayaker used the seif to accelerate and make a sharp turn in the rapid.”