noun
plural -mies
[count] someone who hates another :someone who attacks or tries to harm another
If you are your own worst enemy you act in a way that causes harm to yourself or to the people or things that you care about.
something that harms or threatens someone or something
a group of people (such as a nation) against whom another group is fighting a war - usually singular
a military force, a ship, or a person belonging to the other side in a war - usually singular