flexible, pliable, weak, feeble
輭 centers on a lack of rigidity or strength: something that is flexible, pliable, weak, or feeble. The idea applies to physical objects that bend easily as well as to a lack of force or power.
輭 combines 車 (vehicle, cart) with 耎, which likely contributes the sound and the idea of softness or weakness. The exact historical development of 耎 is uncertain, but the character as a whole expresses a cart that is not rigid or strong.
A cart (車) that is made of soft, pliable material (耎) would be weak and flexible, unable to carry heavy loads. Picture a rickety cart with wheels that bend under weight.
For ゼン, imagine a Zen master sitting calmly on a flexible, weak cart that wobbles but never breaks: Zen -> ゼン, and the cart's pliability reflects the master's adaptable mind.