昌
ショウ, さかん, まさ, まさし, よし, あき, あきら, さかえ, あつ, すけ
prosperous, bright, clear
JLPT1 G13 S0 F1372
Originally, an abbreviated form# of 昜 (bright) + 曰 say/speech indicator → chant/recite in a *bright*/*clear* voice → *prosper* (← bright conditions). A seal inscription form simplifies the character to 曰 + 日 sun/day.
[Full Kanji Etymology List]