Learner's definition of EYEBROW
: the line of hair that grows over your eye
◊ To raise an/your eyebrow is to move your eyebrow up in a way that shows surprise or mild disapproval. To raise eyebrows is to cause other people to react in this way. These phrases are often used figuratively.
No one raised an eyebrow [=no one expressed surprise] when he announced that he was planning to run for governor.
His recent public statements have raised (a few) eyebrows. [=people have reacted with surprise and disapproval to his recent public statements]