Here are some synonyms for "furtive":
* Stealthy
* Clandestine
* Covert
* Surreptitious
* Sly
* Shifty
* Underhanded
Examples:
* The thief cast a furtive glance over his shoulder, making sure no one was watching.
* She gave him a furtive smile, hoping no one would notice.
* His furtive movements aroused the suspicion of the police.
In contrast, "furtive" is often used in comparison to open and honest actions.
For example, a person who is open and honest about their feelings might be described as being forthright, candid, or frank.