This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
焇 combines 火 (fire) with 肖, which likely contributes the sound. The exact historical development is uncertain.
Fire 火 beside 肖 suggests something related to fire, but the exact meaning is unclear. Imagine a fire that melts or erases something, like the readings hint.
For ショウ, picture a fire that can show you how to melt things: show -> ショウ, and the fire 火 on the left is the source of the heat.