1.

peer

Peer is short for superior.

A peer is a platform extending over some body of water.

Peer pressure can have adverse effects on people as they grow up.

2.

alter ego

He has a strong alter ego and always tries to dominate a conversation.

During high school, Pete was my alter ego, but we grew apart later.

"Alter ego" means the same as "self-esteem."

3.

collaborator

A collaborator is a person who cannot work alone.

In many countries, collaboration with the enemy is considered a form of treason and severely punished.

The witness could not collaborate the statements made by the defendant.

4.

congenial

My roommate is truly congenial: she gets perfect scores on every math test and already takes advanced classes.

My congenial roommate puts up even with the mess I make in my corner of the room.

He's a congenial liar and should not be believed on this or any other occasion.

5.

fraternal

Members of a fraternal order are supposed to consider each other brothers.

My fraternal grandfather is still alive and well.

Women and girls cannot have fraternal feelings for other people.

6.

affinity

A shared language immediately establishes a sense of affinity between two nations.

It was with a sense of affinity that we watched our team lose the decisive seventh game.

My affinity for heat is so great that I suffer terribly during hot summer months.

7.

animus

The movie critic was known for her strong animus against movies starring Clint Eastwood.

The animus of my niece for her dog is so great she lets him sleep on her bed.

An animus functions like an alter ego.*

8.

confidant

I am confidant that I will pass the driving test on my next try.

When the band struck up, the confidants decended the grand staircase.

First ladies are sometimes the most important confidant of a president.

9.

enmity

Enmity and animus are opposites.

Enmity between the two parties made it impossible to arrive at a compromise solution.

The enmity between my sister and me has helped me overcome countless crises in my life.

10.

adversarial

In order to make its products better known, the company increased its adversary budget.

A fight over an inheritance or will has turned many siblings into adversaries.

A rapport* between two people is an adversarial relationship.