Spooky (adjective)

1. Relating to ghosts or spirits.
2. Eerie or creepy.
3. Relating to undercover agents, especially for a government.

Origin:

Derived from the noun spook, possibly from the dutch spook ("ghost"), or the low german spōk, spōken ("specte.r")

Examples:

1. The old abandoned house had a spooky feeling to it.
2. The dark forest at night was spooky.
3. The spooky music in the movie made me jump.
4. His spooky behavior made her uneasy.
5. The spooky agent followed them all the way to the border.