The Collaborative International Dictionary of English v.0.48:

Monadelphia \Mon`a*del"phi*a\, n. pl. [NL., from Gr. mo`nos
   alone + 'adelfo`s brother.] (Bot.)
   A Linnaean class of plants having the stamens united into a
   tube, or ring, by the filaments, as in the Mallow family.
   [1913 Webster] Monadelphian