accretion

Increase by natural growth, especially the gradual increase of organic bodies by the internal addition of matter; organic growth; also, the amount of such growth.

Warwick was unable to perceive much change in the market-house. […] There might have been a slight accretion of the moss and lichen on the shingled roof.

The immense accretion of flesh which had descended on her in middle life like a flood of lava on a doomed city had changed her from a plump active little woman with a neatly-turned foot and ankle into something as vast and august as a natural phenomenon.

(Gradual) increase by an external addition of matter; (countable) an instance of this.

Near-synonym: accumulation

A mineral augments not by growth, but by accretion.

(Gradual) increase by an external addition of matter; (countable) an instance of this.

Followed by of: external addition of matter to a thing which causes it to grow, especially in amount or size.

[W]hile ſome fevv grevv rich by turning Money in their ovvn Banks, there vvas a falſe Appearance of VVealth vvithin, but no Accretion of Riches from abroad.

The process of separate particles aggregating or coalescing together; concretion; (countable) a thing formed in this manner.

The accretion of particles forms a solid mass.

[T]he vvhole Country of Holland ſeems to be an Accretion partly by the Sea, partly by the River Rhine.