Decay:
intransitive verb
1
: to decline from a sound or prosperous condition
2
: to decrease usually gradually in size, quantity, activity, or force
3
: to fall into ruin
4
: to decline in health, strength, or vigor
Erode:
nsitive verb
1
: to diminish or destroy by degrees:
a : to eat into or away by slow destruction of substance (as by acid, infection, or cancer)
b : to wear away by the action of water, wind, or glacial ice <flooding
eroded the hillside>
c : to cause to deteriorate or disappear as if by eating or wearing away<inflation
eroding buying power>
2
: to produce or form by
eroding <glaciers
erode U-shaped valleys>