Bosom friend refers to someone who is extremely close to your heart. This term is considered an old-fashioned expression and newer synonyms that are often used in its place include "best buddy", "soulmate", "closest companion", "partner in crime", "kindred spirit", "confidant", "intimate friend", "trusty mate", "amigo", and "beloved friend". Each of these terms reflects a deep and significant connection that is built on trust, love, and mutual understanding. Regardless of how we choose to describe our closest friends, it is comforting to know that we have someone in our lives who we can confide in and share life's ups and downs with.