Where does “downslope” come from?

Downslope is a compound of English down, from Old English dūn (hill), ultimately from Proto-Indo-European dʰewh₂- (to smoke or rise), and English slope.

downslope (English): in a direction down a slope; down a slope; a...

Definitions

in a direction down a slope; down a slope; a...

Ancestry of “downslope”, step by step

downslope traces back through two separate lines of ancestry.

via English Down

Step	Language	Word	Meaning
1	English	Down	usually known as County Down
2	Middle English	doun	down
3	Old English	dūn	hill, down; hill, dune; hill, mountain
4	Proto-Germanic	*dūnā	—
5	Proto-Celtic	dūnom	stronghold, rampart
6	Proto-Indo-European	dʰewh₂-	smoke; mist, haze

via English slope

Step	Language	Word	Meaning
1	English	slope	An area of ground that tends evenly upward or...
2	English	aslope	Slanted or sloping; In an unintended or...
3	Middle English	aslope	—

Every word from Proto-Indo-European dʰewh₂- →