Encroachment, n.
1. The act of entering gradually or silently upon the rights or possessions of another; unlawful intrusion. An unconstitutional encroachment of military power on the civil establishment. Bancroft.
2. That which is taken by encroaching on another.
3. (Law)
An unlawful diminution of the possessions of another.
Shades of meaning
Fernald has no entry of its own for encroachment; he lists it under attack.
He lists it without comment; the entries above explain its neighbors.