General synonyms:
* Companionship
* Fellowship
* Solidarity
* Friendship
* Bonding
* Unity
* Esprit de corps
More specific synonyms:
* Mutual trust (emphasizes the trust between people)
* Shared experience (emphasizes the common ground between people)
* Mutual support (emphasizes the help and encouragement people provide each other)
* Intimacy (emphasizes the closeness and understanding between people)
* Warmth (emphasizes the feeling of friendliness and affection)
The best synonym for you will depend on the specific context in which you are using the word.