The stem of a tobacco pipe.
(chiefly humorous). A thin leg or arm.
More fully "pipestem clematis". US. A white-flowered Californian clematis, Clematis lasiantha.
A white-flowered clematis of the western United States and Canada, Clematis ligusticifolia (the western white clematis).
Of an arm or leg: extremely thin.
Of trousers: tight-fitting, straight.