early 14c., "hard, resinous mineral pitch found originally in Biblical lands," from Late Latin asphaltum, from Greek asphaltos "asphalt, bitumen," often said to be from Greek a- "not" + *sphaltos "able to be thrown down," taken as verbal adjective of sphallein "to throw down," according to Beekes "under the assumption that it denoted the material that protects walls from tumbling down," but he finds this proposed etymology "weak." Perhaps from Semitic [Klein, citing Lewy, 1895] or another non-Greek source.
Meaning "paving composition of tar and gravel" dates from 1847 and its popular use in this sense established the modern form of the English word, displacing in most senses asphaltum, asphaltos. As a verb meaning "to cover with asphalt," from 1872. Related: Asphaltic.