The Collaborative International Dictionary of English v.0.48:

Culm \Culm\ (k[u^]lm), n. [L. culmus stalk, stem; akin to
   calamus. SeeHalm.] (Bot.)
   The stalk or stem of grain and grasses (including the
   bamboo), jointed and usually hollow.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Culm \Culm\, n. [Perh. from W. cwlm knot or tie, applied to this
   species of coal, which is much found in balls or knots in
   some parts of Wales: cf. OE. culme smoke, soot.] (Min.)
   (a) Mineral coal that is not bituminous; anthracite,
       especially when found in small masses.
   (b) The waste of the Pennsylvania anthracite mines,
       consisting of fine coal, dust, etc., and used as fuel. --
       Raymond.
       [1913 Webster]

WordNet (r) 3.0 (2006):

culm
    n 1: stem of plants of the Gramineae