erosion-n; 3 Senses

Sense Number 1: the gradual process of removing material from a surface

Commentary: EROSION[+activity][+process][+gradual][+physical][+removal][+material]
NOTE: refers to an ongoing process, not the physical structure (Sense 3)

The farmers terraced their land to help prevent soil erosion.
Bacteria can cause erosion of tooth enamel.
The road surfaces are subject to erosion and must be repaired regularly.

WordNet 3.0 Sense Numbers: 1, 4

Sense Number 2: gradual decline or diminution of something

Commentary: EROSION[+activity][+process][+gradual][+social][+diminution]
NOTE: a figurative extension of Sense 1
NOTE: implies social, or otherwise abstract deterioration

The erosion of public support of current foreign policy has been noticeable.
They view these trends as evidence of the continuing erosion of moral values.
The industry's poor performance this past quarter has caused an erosion of confidence among investors.

WordNet 3.0 Sense Numbers: 3

Sense Number 3: the resulting state of having removed material from a surface

Commentary: EROSION[+state][+result][+diminished] [+entity][+structure][+damaged][+material]
NOTE: refers to the resulting structure or state, not an activity (Sense 1)
NOTE: you can point to the structure

The geologist pointed out the erosion of the sandstone cliffs to the students.
These erosions of the limestone were caused by water, not by wind.
The surgery revealed areas of gastric erosions in the patient's small intestine.

WordNet 3.0 Sense Numbers: 2