yoke
軛 centers on a wooden crosspiece that joins two animals together for pulling: a yoke. The meaning is concrete and specific to that object.
軛 combines 車 (vehicle) with 厄, which likely contributes the sound and the idea of a yoke or restraint. The exact historical development of 厄 is uncertain.
The left side is a vehicle 車, and the right side 厄 looks like a curved bar with a hook. Picture a wooden yoke attached to a cart, linking the animals to the vehicle.
For ヤク, imagine a yak wearing a yoke: yak -> ヤク, and the strong animal pulls the cart.