Slide51.gifproperly cite a picture C 2004 Robert. A Freitas Jr. (WWW.rfreitas.com)
Mass:

a collection of incoherent particles, parts, or objects regarded as forming one body: a mass of sand.
The American Heritage® Science Dictionary Copyright © 2002. Published by Houghton Mifflin.

Simplified def: The constant weight of an object. It will weigh the same everywhere.
Synonyms: The only real synonym for this word is Accumilation
Antonym: an antonym would be disperse

This word would be easier to remember as long as you know that mass is a constant never changing weight.