When two people are arm in arm, they both have one arm bent at the elbow and passing around and supporting, or being supported by, the arm of the other person.

We walked arm in arm along the river bank. 我们臂挽着臂顺着河岸漫步。

The couple left arm in arm, wandering back towards the church.

The two women strolled arm in arm around the plaza.

Protesters marched arm in arm down the street.

The photo shows Gloria arm in arm with a handsome young man.

See also: arm noun (BODY PART)