Dic: glance// steal a glance at

─. If you steal a glance at someone or something, you look at them quickly so that nobody sees you looking.

• He stole a glance at the clock behind her.

─. To look at someone or something very quickly and discreetly.

• That boy just stole a glance at you again! I think he likes you!
• I stole a glance to see if the teacher was watching us.

─. Fig. to sneak a peek at someone or something.

• He stole a glance at his brother, who appeared to be as frightened as he was.
• Karen stole a glance at her watch and yawned.

....... Cobuild, Farlex Dic of Idioms, McGrow-Hill Dic of American Idioms and Phrasal Verbs.