What is "club root"

Club \Club\ (kl[u^]b), n. [Cf. Icel. klubba, klumba, club, klumbuf[=o]ir a clubfoot, SW. klubba club, Dan. klump lump, klub a club, G. klumpen clump, kolben club, and E. clump.]

1. A heavy staff of wood, usually tapering, and wielded with the hand; a weapon; a cudgel.

   But make you ready your stiff bats and clubs; Rome and her rats are at the point of battle.
   --Shak.

2. [Cf. the Spanish name bastos, and Sp. baston staff, club.] Any card of the suit of cards having a figure like the trefoil or clover leaf. (pl.) The suit of cards having such figure.

3. An association of persons for the promotion of some common object, as literature, science, politics, good fellowship, etc.; esp. an association supported by equal assessments or contributions of the members.

   They talked At wine, in clubs, of art, of politics.
   --Tennyson.

   He [Goldsmith] was one of the nine original members of that celebrated fraternity which has sometimes been called the Literary Club, but which has always disclaimed that epithet, and still glories in the simple name of the Club.
   --Macaulay.

4. A joint charge of expense, or any person's share of it; a contribution to a common fund.

   They laid down the club.
   --L'Estrange.

   We dined at a French house, but paid ten shillings for our part of the club.
   --Pepys.

   Club law, government by violence; lynch law; anarchy.
   --Addison.

   Club root (Bot.), a disease of cabbages, by which the roots become distorted and the heads spoiled.

   Club topsail (Naut.), a kind of gaff topsail, used mostly by yachts having a fore-and-aft rig. It has a short ``club'' or ``jack yard'' to increase its spread.