1.
to fall to the ground :
She tripped and went down with a bump.
2.
if a ship, etc. goes down , it disappears below the water
SYN sink
3.
when the sun or moon goes down , it disappears below the horizon
SYN set
4.
if food or drink will / will not go down , it is difficult / easy to swallow :
A glass of wine would go down very nicely (= I would very much like one) .
5.
if the price of sth, the temperature, etc. goes down , it becomes lower
SYN fall :
The price of oil is going down.
Oil is going down in price.
OPP go up
6.
( informal ) to get worse in quality :
The neighbourhood has gone down a lot recently.
7.
( computing ) to stop working temporarily :
The system is going down in ten minutes.
8.
( NAmE , informal ) to happen :
You really don't know what's going down?