malone,
It took me years to stop reading 'number' as always meaning 1,2,3 etc.
Or to put it another way, to read it with a silent 'b'.
So it could be a verb or an adjective, as well as a noun.
Although in this case it's a noun of course.
It's a crafty old setter's trick but it nearly always gets me.
It was only by following the logic of the clue that I got there - and I had to look up ETHERIST to make sure.