This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
昣 combines 日 (sun) with 㐱, but the exact historical development and original meaning are uncertain. The modern form is rare and its component relationship is unclear.
The left side is 日 (sun) and the right side is 㐱, a shape that appears in several kanji. Without a clear meaning, picture the sun shining through a rare, intricate pattern, making the scene bright and clear.
For シン, imagine the sun (日) shining on a shiny (シン) new object, making it gleam clearly. Shiny -> シン.