foe-n; 3 Senses

Sense Number 1: an opposing military force

Commentary: FOE[+entity][+group][+force][+military][+opposing]

They fought the foe in close quarters, from house to house.
The countries had been allies in the previous war but were now foes.

WordNet 3.0 Sense Numbers: 1

Sense Number 2: a personal adversary, rival, challenger

Commentary: FOE[+entity][+person][+adversary]

He is the senator's most serious political foe in the coming election.
Those football teams have been foes throughout the history of the two colleges.
Anyone Bob perceived as a possible foe was relocated to a different department.

WordNet 3.0 Sense Numbers: 2

Sense Number 3: something perceived to be harmful or injurious

Commentary: FOE[+relation][+role][+harmful]

Let's join forces against the common foe of government waste.
It's a sobering report on toxic waste and other foes to the environment.

WordNet 0.0 Sense Numbers: 4