rarefied

• Although the epithets are more rarefied--here it's "obscurantist" and "crypto-Cartesian" rather than "liberal" or "right-wing"--recent exchanges between neuroscientists and philosophers of mind (and in each group among themselves) feature the same sort of relentless defensiveness and stark opinionated name calling we expect from irate Congressmen or trash-talking linebackers. —  Omni: October 1993
• Objects at fifty miles' distance seem close upon you, so clear and rarefied is the air. —  Travels in the Great Desert of Sahara, in the Years of 1845 and 1846
• Should the angle be too great for the velocity, then the rarefied area over the top of the surface becomes of irregular shape with attendant turbulent eddies. —  The Aeroplane Speaks Fifth Edition
• Again, the rarefied area over the top of the surface is most rare towards the front of it, as, owing to eddies, the rear of such area tends to become denser Illustration Thus, you see, the front part of the surface is the most valuable from the point of view of securing an upwards reaction from the air; and so, by increasing the proportion of front, or "span," to chord, we increase the amount of reaction for a given velocity and area of surface. —  The Aeroplane Speaks Fifth Edition
• If less than that, the air engaged by the bottom of the top surface will have a tendency to be drawn into the rarefied area over the top of the bottom surface, with the result that the surfaces will not secure as good a reaction as would otherwise be the case It is not practicable to have a gap of much more than a distance equal to the chord, owing to the drift produced by the great length of struts and wires such a large gap would necessitate. —  The Aeroplane Speaks Fifth Edition

Roget's II: The New Thesaurus