accession n1 : increase by something added
: the mode of acquiring property by which the owner of property (as a building, land, or cattle) becomes the owner of an addition by growth, improvement, increase, or labor
2 : the act of assenting or agreeing
Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.