Definition of "impermeable" [im•per•me•a•ble]

• Impossible to permeate: an impermeable membrane; an impermeable border. (adjective)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "On the wall hung a simple chart of a rock formation with layers labelled impermeable, source, permeable and reservoir; a list saying things like spudded Oct. '71, plugged and abandoned Jan.' 72; and three brightly coloured maps of the North Sea, each of them showing a different aspect of the oil drilling operations going on there."
• "The old operation of "perineal section" for so-called impermeable stricture is very different, being difficult, dangerous, and uncertain in its results."
• "Many geothermal reservoirs have heat, but the rock is impermeable, which is the problem at the Raft River well known as RRG-9."