tenebrous (ˈte-nə-brəs)
Definition
1. shut off from the light : dark, murky
2. hard to understand : obscure
3. causing gloom
In Context
“By its very nature rather tenebrous, undercover intelligence gathering blurs the lines between procedure and actual process, making it a difficult area to monitor and regulate.”Sarah Vine, Radio Choice; The Times (London, UK); Sep 29, 2012.