restraint
眕 centers on holding back or controlling oneself: restraint. The meaning is narrow and does not extend into broader abstract applications.
眕 combines 目 (eye) with 㐱, which likely contributes the sound. The exact historical development is uncertain, but the eye component suggests a connection to looking or watching, possibly related to restraint through visual control.
The eye 目 on the left watches the right side 㐱, like a stern gaze that holds someone back. Picture a parent's warning look that restrains a child from misbehaving.
For シン, imagine a thin (シン) leash held by the eye's gaze, restraining movement: thin -> シン.