If you're in a fight with a friend and you want to end it, you should make a conciliatory gesture, such as inviting her to a party you're having. Conciliatory describes things that make other people less angry.
The context is often a situation in which a dispute is settled by compromise. A synonym is propitiatory, though this adjective usually refers to avoiding the anger of someone who has the power to harm. In the word conciliatory, the –ory suffix means "relating to or doing," and the root is from Latin conciliatus, from conciliare "to bring together, win over," from concilium "council."