Definitions of elbow:

• noun:   the joint of a mammal or bird that corresponds to the human elbow
• noun:   the part of a sleeve that covers the elbow

  Example: "His coat had patches over the elbows"

• noun:   a sharp bend in a road or river
• noun:   a length of pipe with a sharp bend in it
• noun:   hinge joint between the forearm and upper arm and the corresponding joint in the forelimb of a quadruped
• verb:   shove one's elbow into another person's ribs
• verb:   push one's way with the elbows