1.
If you fall overboard, you fall over the side of a boat into the water.
His sailing instructor fell overboard and drowned during a lesson...
ADV: ADV after v
2.
If you say that someone goes overboard, you mean that they do something to a greater extent than is necessary or reasonable. (INFORMAL)
Women sometimes damage their skin by going overboard with abrasive cleansers...
PHRASE: V inflects
3.
If you throw something overboard, for example an idea or suggestion, you reject it completely.
They had thrown their neutrality overboard in the crisis.
PHRASE: V inflects