What does "brier" mean?

Brier: Fig.: Anything sharp or unpleasant to the feelings. The thorns and briers of reproof. Cowper. Brier root, the root of the southern Smilax laurifolia and S. Walleri; -- used for tobacco pipes. -- Cat brier, Green brier, several species of Smilax (S. rotundifolia, etc.) -- Sweet brier (Rosa rubiginosa). See Sweetbrier. -- Yellow brier, the Rosa Eglantina.