The word down has many uses. It can be a preposition or an adverb particle.
Down can mean from a higher to a lower level.
The sun went down.
It can also mean from an upright to a lying position.
I want to lie down.
The boy was knocked down by a car.
While up is used for movement to a more important place or position, down is used for movements in the opposite direction.
He has gone down three places in the class.
They have gone down to the country for a holiday. (Movement from the city to the country)
They are going up to Singapore for a holiday. (Movement from the country to the city)
The temperature has gone down.
Down can also mean ‘on paper’.
Put your name down for a ticket. (= Put your name on paper for a ticket.)
To put your foot down is to insist.
She put her foot down and made him change his mind.
Be down and out = exhausted, beaten
Downright = honest, straightforward or thorough
It is downright hypocrisy.
To pay $10 down is to pay $10 now and the rest later.
Downtown = to or in the main or business part of town
Downfall = ruin or sudden fall from fortune or power