Accretion

1) in real estate, the increase of the actual land on a stream, lake or sea by the action of water which deposits soil upon the shoreline. Accretion is Mother Nature's little gift to a landowner.  Compare to avulsion and alluvion.

2) In estates, when a beneficiary of the person who died gets more of the estate than he/she was meant to because another beneficiary or heir dies or rejects the gift. Example: if a brother and sister were supposed to divide a share of Dad's estate, but brother doesn't want it, then sister's share grows by accretion.

3) In trusts, accretion occurs when a beneficiary gets a surprising increase in benefits due to an unexpected event.

- Law.com