Obviously both are the very same thing. I'd suggest to merge them and converting the remaining one (depending on which is the merging target) into a synonym.
I believe that these are actually different things:
wifi-hotspotcould represent any wifi network, or a public 'wifi hotspot'.
wifi-tethering would mainly represent the actual process of tethering, or creating a hotspot.
As such, I don't think they should be merged.