Where does “upstair” come from?

upstair (English) comes from English stair, from Middle English steire, from Old English stǣġer, from Proto-Germanic staigriz, from Proto-Indo-European steyǵʰ- — to go.

upstair (English): upstairs

Definitions

upstairs

Ancestry of “upstair”, step by step

upstair traces back through two separate lines of ancestry.

via English stair

Step	Language	Word	Meaning
1	English	stair	A single step in a staircase; A series of steps;...
2	Middle English	steire	staircase, stairs; stair, step; ladder
3	Old English	stǣġer	stair, staircase
4	Proto-Germanic	staigriz	scaffold, platform; stairs
5	Proto-Indo-European	steyǵʰ-	to go

via English up

Step	Language	Word	Meaning
1	English	up	Away from the surface of the Earth or other...
2	Middle English	up	to a vertical axis
3	Old English	upp	up; upstairs
4	Proto-West Germanic	*upp	—

Every word from Proto-Indo-European steyǵʰ- →Every word from Proto-Germanic staigriz →Every word from Old English stǣġer →