This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
睲 combines 目 (eye) with 星 (star), but the exact historical development and original meaning are uncertain.
The left side is an eye 目 and the right side is a star 星. Imagine an eye that shines like a star, but the actual meaning is unclear.
For セイ, picture a starry eye that can see clearly: say -> セイ, as if the eye says 'I see stars'.