Fraternize (verb)

To associate or mix socially as friends or equals, especially with people of a different social group, race or profession.

Origin:

Early 19th century: from french fraterniser, from fraternel "fraternal".

Examples:

1. The soldiers were forbidden to fraternize with the local population.
2. The company's policy prohibited employees from fraternizing with clients.
3. He was accused of fraternizing with the enemy.
4. The students fraternized with the other teams during the tournament.
5. The two groups fraternized with each other and formed a friendship.