Located or occurring beneath a shell.
A shell that lies beneath another shell; a subsidiary layer within a shell.
A set of allowed quantum states within a shell of an atom which can be occupied by electrons having the same value of the orbital quantum number l. Also: a corresponding set of allowed quantum states of nucleons in a nucleus.
An instance of a shell initiated by another shell.
Mid 19th century; earliest use found in Annals and Magazine of Natural History. From sub- + shell.