furtive

furtive \FUR-tiv\, adjective:

1. Done by stealth; surreptitious; secret; as, a furtive look.
2. Expressive of stealth; sly; shifty; sneaky.
3. Stolen; obtained by stealth.
4. Given to stealing; thievish; pilfering.

He had always been more than willing to show me parts of [his notebook], whenever I asked him to; and naturally I had taken many furtive looks at its innermost pages when he wasn't around.
-- Michael Chabon, Werewolves in Their Youth

Exchanging furtive glances, they oozed a nervousness, perhaps in fear that some prewritten script would go awry.
-- Michael Bloomberg, Bloomberg by Bloomberg

Why did he keep looking around at all the other tables like that? It made him seem furtive, as if he didn't belong here, as if he were an intruder in so fine a place as this.
-- Mary McGarry Morris, Fiona Range

Furtive is from Latin furtivus, from furtum, "theft," from fur, "thief."