Culm
/kʌlm/noun
mass noun
1- Geology a series of Carboniferous strata in SW England, mainly shale and limestone with some thin coal seams【地质】碳质页岩。
1.1
culm
archaic coal dust or slack〈古〉（无烟）煤屑。
词源
Middle English （in the sense 'soot, smut', now only Scots）： probably related to COAL.