[for something] to decline and grow worse and worse. This industry is going downhill. We lose money every year.As one gets older, one's health tends to go downhill.
to gradually become worse The area has started to go downhill economically in the last ten years.We started to argue soon after we got married, and things went downhill from there.
Deteriorate, worsen, as in Ever since the recession began, the business has been going downhill. The figurative use of downhill for "decline" dates from the mid-1800s. Also see downhill all the way.