foe:
(plural: ‘foes‘; the word opposite in meaning to this word is ‘friend‘ or ‘ally’; pronunciation: ‘foe’ rhymes with the word “toe”)

two soldiers with their foe
a military enemy — a person or army belonging to the country that is at war with one’s own country; an enemy;
a personal enemy — a person whom one hates; a rival;
a player with whom one plays a game or match against; an opponent;
the main contest with whom a contestant is going to compete in a contest or competition; a competitor;
a person who has different or opposite social or political ideas, principles, etc.; an adversary,

two bitter professional foes
Billy had always thought that George was his friend and Daniel was his foe until there came a time when he needed the most support, and then he realised that he had been wrong all along: Daniel was his real friend and George was his worst foe.

two foes fighting for a title
There are different kinds of foes: political foes, who have different political ideologies; personal foes, who have different ideas or preferences; professional foes, who work as colleagues but fight for the best position in the office or organisation; business foes, who fight for best bargains and most profits; and so on.
The political foes are the worst of all the foes because when it is time for the election campaign each candidate tarnishes the other, inspiring the sheepish public to hate so and so and love so and so, but when two or three of the same candidates happen to meet at a private or social gathering, they are so friendly — huggings, handshakings, kisses and praises and back-pattings — that the same public are made to look foolish for quarrelling among themselves for such scoundrels.

Political foes Anna Bligh and Campbell Newman, Townsville, Australia, bitter foes but all smiles and warm hand-shakes!
for an informative article in which we see this word and its different opposite words in meaning are used, please click here,
for an article that talks about google being a friend or foe to the open internet, please click here,
for an item of news that shows us this word is used in the political arena, please click here & please click here,
and
for an article that shows us how this word is also used to refer to non-living things, please click here.
