Down

A down is a hill, usually made of chalk and in southern England. See downland.
Down is the negative direction along the z-axis . Up and down are the only two well-defined directions in the presence of gravity. Earlier this was adown, meaning "from the hill".
Down syndrome is a genetic disorder
County Down is a county in Northern Ireland
Down is a district in Northern Ireland
Down feathers are the fine undercoat of birds under the visible exterior feathers, and is often used as insulation in clothing.
Downe is a village in Kent, where Charles Darwin's house, Down House is.
Mammals have an undercoat sometimes called down hair.
Down, used in American football, is a stage of play; four downs are allowed in a "possession"; three downs are allowed in Canadian football. The reference is to the ball or ball carrier being brought to a halt, often by being knocked down.
Down is a colloquial synonym for depressed or blue.
A computer (or other) system can go down when it essentially loses power or crashes.
There is a heavy metal band named Down.
Down is also a song by Blink 182. The song's video, made in 2004, features many former gang members who a part of an agency that talk people out of gangs and into entertainment industry.