Dictionary.net

• (physics) the theory that any two particles of matter attract one another with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them

2006 - WordNet 3.0
By Princeton University

• (physics) the theory that any two particles of matter attract one another with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them

2011 - English Dictionary Database
By DataStellar Co., Ltd