rust, corrosion
鏥 centers on metal decay: rust and corrosion, the gradual breakdown of metal surfaces.
鏥 combines 金 (metal) with 宿, which likely contributes the sound シュウ and may hint at metal that has 'settled' into a corroded state. The exact historical development is uncertain.
Metal 金 that has been left out in the elements, like an old inn 宿, slowly rusts and corrodes.
For シュウ, imagine a rusty metal shoe left outside an inn: shoe -> シュウ, and the metal 金 rusts like an old shoe.