> Could someone please tell me what the norse word for "rider" is?
> I've found the verb "ridha" -- "to ride" -- so I thought "rider" might be "ridhr" but I'm not sure.

'Riddari' or 'ríðari' but both suggest "knight".

Two common modern compounds are 'reiðmaður' and 'hestamaður'.

Kveðja,
Haukur