サン, たす.ける, たた.える
approve, praise, title or inscription on picture, assist, agree with
JLPT3 G5 S15 F868
兟# is 先 (advance in small increments) doubled → group advancing in small increments. 贊 adds 貝 commodities → collect/accumulate presents from supporters in small increments → *support* → *praise* (← verbal support) → *panegyric*; *eulogy*; *inscription*; *dedication*. There is no etymological connection between the Shinjitai 賛 and 替.
[Full Kanji Etymology List]