To cut off the head of a person or animal. The executioner was ordered to decapitate the prisoner at dawn.
To undermine or remove the leadership or top management of an organization or group. The scandal threatened to decapitate the company's board of directors.
To remove the uppermost part of something, such as the blossom of a flower or the crown of a tree, by cutting it off. The gardener accidentally decapitated several tulips while trimming the hedge.