stake, post, picket, piling
杙 centers on a pointed piece of wood driven into the ground: a stake, post, picket, or piling used for support or marking.
杙 combines 木 (tree/wood) with 弋, which likely contributes the sound and may relate to a pointed object. The exact historical development is uncertain.
A wooden 木 stake with a 弋-shaped notch or mark: 杙 is a wooden post driven into the ground.
For ヨク, imagine a wooden stake being used to yoke two animals together: yoke -> ヨク, and the stake keeps them in place.