window seat

WordReference Random House Unabridged Dictionary of American English © 2025

win′dow seat′, 

1. Architecture a seat built beneath the sill of a recessed or other window.
2. Furniture a bench having two arms and no back.
• 1745–55

Collins Concise English Dictionary © HarperCollins Publishers::

window seat noun

1. a seat below a window, esp in a bay window
2. a seat beside a window in a bus, train, etc