n.1 growth by organic enlargement.
2 a the growing of separate things into one. b the product of such growing.
3 a extraneous matter added to anything. b the adhesion of this.
4 Law a ACCESSION. b the increase of a legacy etc. by the share of a failing co-legatee.
Derivatives:
accretive adj.
Etymology: L accretio (as ACCRETE)