a gate that controls the flow of water into a canal lock, sluice, etc.
head gate in American English
noun
1.
a control gate at the upstream end of a canal or lock
2.
a floodgate of a race, sluice, etc
Word origin
[1830–40, Amer.]This word is first recorded in the period 1830–40. Other words that entered Englishat around the same time include: isomerism, orientation, rococo, showcase, stroboscope