What does Genesis 37:19 mean?

Jacob, renamed Israel by God (Genesis 35:10), was raised by parents who displayed obvious favoritism (Genesis 25:27–28). That contributed to rivalry and tension with his twin brother, Esau. Seeming to learn nothing from this, Jacob has lavishly favored his son, Joseph, over his other children (Genesis 37:3–5). This resulted in deep resentment. Joseph, for his part, has naively inflamed those emotions (Genesis 37:2), especially by talking about his audacious dreams (Genesis 37:5, 9). Joseph's brothers are capable of terrible violence (Genesis 34:26–27). And yet, Jacob has sent Joseph far from the safety of home to bring back a report on these men (Genesis 37:12–17).

As Joseph approaches his brothers' camp, they are plotting to murder him in cold blood (Genesis 37:18). Sarcastically, they refer to him as a "dreamer," referring to Joseph's self-reported dreams about ruling over all of them. They have hated him for some time because of his dreams and because of their father's clear preference for him. Now they are ready to act on that hatred.