bi·tu·men (bĭ-tōō'mən, -tyōō'-, bī-) n. Any of various flammable mixtures of hydrocarbons and other substances, occurring naturally or obtained by distillation from coal or petroleum, that are a component of asphalt and tar and are used for surfacing roads and for waterproofing.
[Middle English bithumen, a mineral pitch from the Near East, from Latin bitūmen, perhaps of Celtic origin.] bi·tu'mi·noid' (-mə-noid') adj.
1460, from L. bitumen "asphalt," probably, via Oscan or Umbrian, from a Celtic source (cf. Gaulish betulla "birch," used by Pliny for the tree supposedly the source of bitumen). Bituminous is from 1620.