weight
硾 centers on the idea of weight, specifically a heavy object used to press down or add mass.
硾 combines 石 (stone) with 垂, which likely contributes the sound and suggests hanging or pressing down, giving the idea of a stone weight.
A stone 石 on the left and 垂 (hanging down) on the right: picture a heavy stone weight hanging from a rope, pressing down firmly.
For ツイ, imagine a heavy stone weight swinging on a rope and making a 'tsui' sound as it hits the ground: tsui -> ツイ.