The Collaborative International Dictionary of English v.0.48:

Limonite \Li"mon*ite\ (l[imac]"m[o^]n*[imac]t), n. [Gr. leimw`n
   any moist grassy place, a meadow: cf. F. limonite, G.
   limonit.] (Min.)
   Hydrous sesquioxide of iron, an important ore of iron,
   occurring in stalactitic, mammillary, or earthy forms, of a
   dark brown color, and yellowish brown powder. It includes bog
   iron. Also called brown hematite.
   [1913 Webster]

WordNet (r) 3.0 (2006):

limonite
    n 1: a widely occurring iron oxide ore; a mixture of goethite
         and hematite and lepidocrocite