as thick as thieves

Meaning

• a very secretive and close relationship between people.
• people as thick as thieves usually share confidences, are great friends, and spend much time together.
• intimate
• closely allied
• familiar
• sharing confidences
• people with a close association excluding the general population.

Examples in Sentences

1. They remained as thick as thieves for several weeks. This made us curious to know what they were doing.
2. The foal appears great, and since it is the second to be born here in the space of a week, we're confident the two new arrivals will be as thick as thieves. ...