shell

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shell

(shel),
An outer covering.

shell

Etymology: AS, scell
1 a hard outer protective covering that encloses material.
2 a principal energy level occupied by an electron in an atom.

shell

(shel)
An outer covering.

shell

any hard outer covering, such as the carapace of turtles and tortoises, the exoskeleton of crustaceans, the calcareous plates of echinoderms, the outermost membranes of an egg, the skeleton of Foraminifera or the mantle secretions of molluscs.

impression, eye

A negative form or replica of the anterior part of the eye. A substance with rapid gelling properties is held in contact with the eye until gelled. This impression (or mould) is then used in the preparation of a positive model called a cast (or casting) of the anterior part of the eye: it is made by filling the impression with a material containing a plaster of Paris base which hardens to artificial stone. Using this cast a shell of a scleral contact lens is produced with optimum shape of the back surface. Syn. impression; impression moulding; mould; ocular impression.
References in periodicals archive ?
Why abandon the DOS C:\> prompt, familiar batch file menus or DOS shells, and tried-and-true software applications for a newfangled, upstart graphical environment?
Although DOS shells and menu programs allow one to avoid DOS, they differ in the kind of options they make available.
It's obvious that the DOS Shell is an attempt to place a graphical interface on a text-based system.
It does this without the operating overhead and loss of memory typical of GUIs, DOS shells, and other intervening software.