Surreptitious

Spenser would not tell anyone his surreptitious plan to get back at his friends for pranking him.

There is more than a fine line between unspoken rizz and surreptitious sexual harassment.

The surreptitious gesture went unnoticed by the rest of the room.

He read the letter aloud. Sophia listened with the studied air of one for whom, even in these days, a title possessed some surreptitious allurement.

It is also worth noting the case law on prisoners' correspondence which establishes that interception of a person's communications need not be surreptitious in order to amount to an interference with respect to Art 8 (1) [ECHR].