Stool

A stool was a type of seat, that one could sit on.

In a police box, there was often a writing desk and stool, as well as an electric heater. (AUDIO: The Eternal Summer)

Altos was once hit over the head with a stool. (TV: The Keys of Marinus)

The Seventh Doctor's question-mark umbrella handle was known to split in half and unfold into a seat, allowing the Doctor to plant the umbrella into the ground and use it as a makeshift stool. (COMIC: Planet of the Dead, PROSE: Storm Harvest)

Iris Wildthyme once had a bar stool on the Celestial Omnibus. (PROSE: Enter Wildthyme)