偷偷 (tōu tōu): ลักลอบ

While his mother wasn't looking, he stealthily slipped the candy into his pocket.

During class, she stealthily read a novel under her desk, afraid of being caught by the teacher.

To surprise his girlfriend, he secretly prepared a ring and planned to propose on her birthday.

The thief stealthily sneaked into the house, but was caught clearly on the surveillance camera.

She stealthily approached the cat from behind, wanting to pet it, but the cat still ran away.