adv., adj., & n.
--adv. in a descending direction, esp. towards the bottom of an incline.
--adj.
1. sloping down, descending.
2 declining; deteriorating.
--n.
1. Skiing a downhill race.
2 a downward slope.
3 a decline.
Phrases and idioms:
go downhill colloq. decline, deteriorate (in health, state of repair, moral state, etc.).