Noun

• S: (n) downhill (the downward slope of a hill)
• S: (n) downhill (a ski race down a trail)

Adjective

• S: (adj) declivitous, downhill, downward-sloping (sloping down rather steeply)
• similar to
• derivationally related form
• antonym

Adverb

• S: (adv) downhill (toward a lower or inferior state) "your performance has been going downhill for a long time now"
• S: (adv) downhill (toward the bottom of a hill) "running downhill, he gained a lot of speed"