surreptitious
adjective uk/ˌsʌr.əpˈtɪʃ.əs/ us/ˌsɝː.əpˈtɪʃ.əs/
秘密的，偷偷的；鬼鬼祟祟的
done secretly, without anyone seeing or knowing
She seemed to be listening to what I was saying, but I couldn't help noticing her surreptitious glances at the clock. 她看起来好像在听我说话，但我明显注意到她偷偷看了几眼钟。