This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
暛 combines 日 (sun) with 差, which likely contributes the sound. The exact historical development is uncertain.
The sun 日 beside 差 suggests something related to light or clarity, but the exact meaning is unclear. Picture the sun shining on a difference, making it bright and clear.
For サ, imagine the sun (日) shining on a difference (差) and making it clear: the sound 'sa' is like the first part of 'sun' and 'difference' combined, but use the Japanese reading サ as in さあ (saa, come on) when the sun comes out.