obscuration

obscuration (countable and uncountable, plural obscurations)

1. The state of being obscured.
   • 1843, Thomas Carlyle, Past and Present, book 3, ch. X, Plugson of Undershot

     Money is miraculous. What miraculous facilities has it yielded, will it yield us; but also what never-imagined confusions, obscurations has it brought in; down almost to total extinction of the moral-sense in large masses of mankind!

2. A unit of measurement used in particular for smoke detectors which respond to absorption of light by smoke, in percent absorption per unit length, e.g. % obs/ft, % obs/m.