Inherited from Middle English spyinge, spiyng, spyeng, equivalent to spy + -ing.
Meanings
(countable, uncountable) espionage; the act of secretly gathering information
There are two ways in which the obsessive character of jealousy tends to exert itself: one is in the need to know, the endless tests and investigations and spyings that are so characteristic of jealousy. 1980, Amélie Rorty, Explaining Emotions, page 472: