WATER mainly UK (also US faucet) › the part at the end of a pipe which controls the flow of water: the cold/hot tap to turn a tap on/off She rinsed the cup under the tap.
KNOCK › a gentle knock or touch, or the noise made by knocking something gently: I felt a tap on my shoulder. There was a tap at the door.
TELEPHONE › a small piece of equipment that can be fixed to someone's telephone in order to listen to their telephone calls
on tap › easily available: They have all that sort of information on tap.