Furtive

/ˈfɜːr.tɪv/ adjective medium

Done secretly or slyly to avoid being noticed.

She cast a furtive glance at her phone under the table, hoping the teacher wouldn't notice.

Memory Trick

Furtive sounds like 'for thieves' — furtive behavior is the sneaky, hush-hush kind you'd expect from someone trying hard not to get caught.