Heap, pile, stack, shock, cock, mass, bank are comparable as verbs when they mean to bring together into a more or less compact group or collection a number of things and as nouns when they denote the group or collection so assembled.
Heap is the least definite in its implications; it usually implies a moundlike shape and more or less careless or fortuitous arrangement; it may or may not imply a personal agent, an assemblage of like things, close packing, or a large quantity.
Pile distinctively implies the laying of one thing or one layer on top of another in a more or less orderly formation; it usually implies a personal agent and an assembling of like things or things of approximately the same size or shape.
Stack more strongly implies orderly and compact arrangement and the assembling of like things; it almost invariably suggests personal agency and a particular shape or form, and it has a distinctly restricted range of idiomatic reference. Thus, one stacks hay, straw, or grain in the sheaf into conical or a four-sided, round-cornered formation designed to shed rain; one stacks firewood by arranging the pieces neatly into a rectangular pile; one stacks arms when one sets up rifles so that they form a pyramid; one stacks lumber by so arranging it in a pile that air may circulate and warping be minimized.
So strongly does stack suggest care in arrangement that it carries specific connotations in some of its applications; thus, to stack cards is to arrange them secretly for cheating; a stack is in Great Britain a measure of stacked coal or firewood equal to four cubic yards. Shock and cock are the narrowest of these terms.
Shock is used primarily of sheaves of grain (as wheat, rye, or oats) or of stalks of Indian corn which are stacked upright with butt ends resting on the ground.
Occasionally it, like cock, is used with reference to hay stacked in a conical pile.
Mass (see also mass n under BULK ) usually suggests amorphousness; it also implies either a capacity in the things which are brought together for cohering with or adhering to each other so as to form a blended or fused whole or a highly compact or dense agglomerate, or an external process which forces them to cohere or adhere; thus, a pasty substance used in making up pills and troches is called a mass by pharmacists; some flowers (as violets) tend to grow in masses or to mass themselves in growing; to mass colors in a painting or in stained-glass windows is to combine the various colors used in any one significant portion of the whole so that they seem to flow into each other and give a unitary effect when the painting or window is viewed in perspective. Mass, therefore, usually implies integration, but it may be a physical, a spiritual, an emotional, an intellectual, or a purely aesthetic integration.
Bank (the verb is often followed by up ) is used chiefly in reference to substances which when affected by moisture, freezing, or pressure form, or seem to form, into compact masses.