bulk 
(bŭlk)
(bŭlk)n.
1. Size, mass, or volume, especially when very large.
2.
a. A distinct mass or portion of matter, especially a large one: the dark bulk of buildings against the sky.
b. The body of a human, especially when large or muscular.
3. The major portion or greater part: "The great bulk of necessary work can never be anything but painful" (Bertrand Russell).
4. See fiber.
5. Thickness of paper or cardboard in relation to weight.
6. A ship's cargo.
v. bulked, bulk·ing, bulks
v.intr.
1. To be or appear to be massive in terms of size, volume, or importance; loom: Safety considerations bulked large during development of the new spacecraft.
2. To grow or increase in size or importance.
3. To cohere or form a mass: Certain paper bulks well.
v.tr.
1. To cause to swell or expand.
2. To cause to cohere or form a mass.
adj.
Phrasal Verb: Being large in mass, quantity, or volume: a bulk buy; a bulk mailing.
bulk up
Idiom: To gain weight by gaining muscle: dietary supplements that helped the weightlifters bulk up.
in bulk
1. Unpackaged; loose.
2. In large numbers, amounts, or volume.
[Middle English, perhaps partly alteration of bouk, belly, trunk of the body (from Old English būc) and partly from Old Norse bulki, cargo, heap; see bhel-2 in the Appendix of Indo-European roots.]