(verb)
to lower oneself from a superior status, rank, or state of dignity, or to lower one's moral standards in order to do something that one would otherwise find objectionable;
e.g. I would never stoop to the level of treating them so poorly.
(verb)
in old usage, to descend from a great height, especially to dive or swoop down in order to attack or seize prey (used to refer to birds of prey);
e.g. We watched the hawk stoop to catch a rat in its talons.
(noun)
the action of bending the head, shoulders, and/or back forwards and downwards, either temporarily (such as to fit into some space) or permanently (as a posture);
e.g. The man developed a stoop as he grew older and weaker.
(noun)
an instance of a bird of prey descending or swooping down to catch prey;
e.g. He captured the eagle's swoop on camera.
(noun)
a structure such as a veranda, porch, or entrance stairway at the front of a house or some other building;
e.g. They sat on the stoop and enjoyed cups of tea.