This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
熢 combines 火 (fire) with 逢, which likely contributes the sound ホウ. The exact historical development is uncertain.
Fire 火 beside 逢 suggests a fire that meets or encounters something, but the intended meaning is obscure. Think of a signal fire or beacon, as hinted by the reading のろし.
For ホウ, imagine a fire that howls when it meets the wind: howl -> ホウ, and the fire 火 meets 逢 the wind.