Does anyone have an idea of when the word "intelligence" was first used, in the context of espionage? Was it used in this context in (for instance) the 18th century?
According to Etymonline, the usage seems to pre-date the 1580s (assuming the agent noun came after the mass noun with the corresponding sense):
1580s, "spy, informant," agent noun from intelligence.
Meaning "bringer of news" is from 1630s; as a newspaper name from 1640s.
Indeed, Etymonline actually gives the 1580s as the time the 'military intelligence' sense originated. I'd assumed it didn't, as this now becomes general reference.