Meanings of slippery horsehair in English

I sat upright in my slippery horsehair chair and spoke no word.

They sat down on the slippery horsehair, and talked softly and quickly.

But he led her gently to the sofa, and sat down beside her on the hard old slippery horsehair.

There she was, sitting opposite Miss Gallup on one slippery horsehair "easy chair," while her hostess, much beshawled, cushioned and foot-stooled, sat on the other.