downhill; downward slope; descent
decline; waning; ebb; (going) downhill
急な下り坂で自転車が加速した。
The bicycle picked up speed on the steep downhill slope.
下り坂では速度の出し過ぎに注意が必要だ。
On downhill slopes, you need to be careful not to go too fast.
体力の衰えを感じ始めてから、健康状態が下り坂になった。
After I started feeling my strength decline, my health went downhill.