Orpington, according to Bernard Deeprose of Arizona, was originally 'Orpin's Tun'. Orpin was chosen by the Romans to oversee a tun or 'hundred' originally centered in the area of Goddington.(another tun?)
Otford means literally Ottas ford, in this case over the River Darent, and was first recorded as long ago as 832 in the form Otteford. Dartfords name also reflects the fording of the Darent.