Surreptitious

/ˌsʌrəpˈtɪʃəs/ adjective hard

Done secretly and quickly in order to avoid being noticed.

She took a surreptitious glance at her phone under the table during the meeting.

Memory Trick

Surreptitious comes from Latin 'surripere,' to snatch secretly -- think of someone surreptitiously grabbing a cookie the instant no one is looking.