tenuity

tenuity \tuh-NOO-i-tee, -NYOO-, te-\, adjective:

1. thinness of consistency; rarefied condition.
2. the state of being tenuous.
3. slenderness.

The exceeding tenuity of the object of our dread was apparent; for all heavenly objects were plainly visible through it.
-- Edgar Allan Poe, "The Conversation of Eiros and Charmion," 1839

There was no doubt left to me; the atmosphere of the moon was either pure oxygen or air, and capable therefore—unless its tenuitywas excessive—of supporting our alien life.
-- H.G. Wells, The First Men in the Moon, 1901

Tenuity is derived from the Latin word tenuitās meaning "thinness."