The adjacent regular seat is made available to a companion.

An older woman in the adjacent seat put her hand on his shoulder.

She'll meet you on the plane; you've got adjacent seats.

In fact, except for a couple snuggled together, no one sat on adjacent seats.

The pistol remained on the adjacent seat, under his sports coat.

He hesitated, glancing at the young human woman in the adjacent seat.

He looked next to him, but found the adjacent seat empty; there was no trace of his sister, or her remains.

He leaned close to his lieutenant in the adjacent seat.

Leigh-Cheri looked at the old woman asleep in the adjacent seat.

It is usually the person in the adjacent seat complaining about any overspill.