While they all refer to land extending into water, they do have differences:
A cape = A large mass of land extending into a body of water, such as the Cape of Good Hope, Cape Cod, Cape Verde etc.
A promontory is a prominent mass of land which overlooks lower lying land, or a body of water [Cliffs are promontories]
A peninsula is land that is nearly surrounded by water but is connected to the mainland by a neck of land.
A headland is an area of land adjacent to water on three sides.
A point is a projecting, usually tapering piece of land, or a sharp prominence over water.
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