Nemesis vs. enemy (nouns) – An enemy (EN-uh-mee) is a foe that you can defeat or who can defeat you. A nemesis (NEM-us-sis) is unconquerable, a lifelong opponent or rival.
Example for enemy: “The supreme art of war is to subdue the enemy without fighting.” – Sun Tzu
Example for nemesis: “It’s not easy being number two. As a marketer, you have limited choices – you can pretend you’re not defined by the market leader, or you can embrace your position and go directly after your nemesis.” – John Battelle