foot
part of the body
Your foot is the part of your body at the end of your leg. Your foot includes your toes.
He kept on running despite the pain in his foot.
When you use foot with this meaning, its plural is feet.
She's got very small feet.
If someone goes somewhere on foot, they walk, rather than using some form of transport.
The city should be explored on foot.
measurements
A foot is also a unit for measuring length, equal to 12 inches or 30.48 centimetres. When foot has this meaning, its usual plural is feet.
We were only a few feet away from the edge of the cliff.
The planes flew at 65,000 feet.
However, you can use foot as the plural in front of words like high, tall, and long.
She's five foot eight inches tall.
You always use foot as the plural in front of another noun. For example, if a gap is twenty feet wide, you refer to it as a ‘twenty foot gap’. Don't refer to it as a ‘twenty feet gap’.
The prison was enclosed by a forty foot wall.