valve 
/ˈvælv/ noun
plural valves /ˈvælv/ noun [count] 1 : a mechanical device that controls the flow of liquid, gas, etc., by opening and closing
▪ They turned off the main water valve to the house. — see picture at plumbing; see also safety valve 2 : a device in some musical instruments (such as trumpets) that you press to play different notes — see picture at brass instrument 3 medical : a structure in the heart, stomach, etc., that temporarily stops the flow of fluid or that allows fluid to move in one direction only
▪ a heart valve 4 Brit : vacuum tube
▪ They turned off the main water valve to the house. — see picture at plumbing; see also safety valve
▪ a heart valve
