Select the most appropriate meaning of the given idiom.

Thick as thieves

Having a close friendship

The most appropriate meaning of the idiom "thick as thieves" is having a close friendship.

The other options are incorrect.

• "Being very dishonest" does not necessarily mean that two people are close friends.
• "Never helping anyone" does not necessarily mean that two people are close friends.
• "Telling lies all the time" does not necessarily mean that two people are close friends.

The idiom "thick as thieves" comes from the idea that thieves often have to work together and trust each other very closely. In the same way, two people who are thick as thieves are people who are very close friends and trust each other very much. For example, you might say that two best friends are thick as thieves.