Regularly sickest going uphill? Go downhill! (3)
I believe the answer is:
ski
'regularly sickest going uphill? go downhill' is the definition.
I know that 'downhill' relates to this answer. I also know that both the answer and definition are singular nouns
'uphill? go downhill' is the wordplay.
'uphill?' becomes 'slope' (uphill is a kind of slope).
'go' suggests deleting specific letters.
'downhill' becomes 'ski slope' (I've seen this before).
'skislope' with 'slope' taken out is 'SKI'.
Can you help me to learn more?
(Other definitions for ski that I've seen before include "Participate in winter sport" , "Winter sport attachment" , "Runner for use on snow" , "Glide ove snow" , "Snow-runner" .)