§ Thanador >> Ulthanador >> Borthendor >> Orothan[ador] (RS:434)
These are earlier names of later Rohan.
An obviously frequent element contained in three of them is #thana. There is a later root THĂN- ’kindle, set light to’ (MR:388, PE17:187), but the meaning does not fit at all. Intitial th- in Noldorin/Sindarin can also be produced by ST-. The Etymologies give STAN- ’fix, indicate, decide’ with N. thand, thann ’firm, true, abiding’ (VT46:16), Q. sanya ’regular, law-abiding, normal’. The meaning ’firm people’ referring to the character or attitude would make sense. However, to get a word like thana with a final vowel in Noldorin one needs a stem expansion in -G (*thanaga), compare the very similar N. thala ’stalwart, steady, firm’ < ON stalga (STÁLAG-).
Perhaps Tolkien had decided to alter these roots or maybe the final vowel -a survives in the compound medially, as it does e.g. in Magladhûr ’Black-sword’ (MAK-), while it is lost in the isolated word finally: makla > N. magl, magol ’sword’.
Hence, Thanador would mean *’land of firm ones’ < #than(a) *’stalwart, firm’ + dôr ’land, dwelling-place, region where certain people live’ (NDOR-, VT45:38).
The second form further contains the prefix ul-. In The Etymologies under ÚLGU- (ÚLUG-) some Easterling names devised by Elves are listed with this prefix: Ulfang, Uldor, Ulfast, Ulwarth and it must mean ’hideous, horrible’. Indeed, we get to know that the Horse-kings have long been in the service of Sauron, although this conception was apparently quickly changed.
Already the next form contains #borthen, probably a derivate from the stem BOR- ’endure’ with N. boron ’steadful, trusty man, faithful vassal’ and names of ’Faithful Men’ – Bór, Borthandos (Borth + handos), Borlas, Boromir. So #borthen could be the adjective *’trusty, faithful’; Borthendor = *’land of faithful ones’. For the formation compare N. malthen ’of gold’ (SMAL-).
The last form then seems to contain a prefix oro- *’high’, appearing in The Etymologies as or- in orchall, orchel ’superior’ (ORO-). As the end of the word is put into brackets, however, we must assume that Orothan may already stand as a name; on the same page is actually written: Rohan = Rochan(dor) ’Horseland’. Then, Orothan would contain the same suffix -an for ’land’ (Tolkien translates Rohan < Rochann < S. roch ’horse’ as ’Hippia’ in Let:144), leaving the basic form #oroth-, perhaps a noun comparable to N. meleth ’love’ from MEL- or tirith ’watch, guard’ from TIR-. Hence – Orothan *’land of exalted ones’? Or does it simply refer to the terrain – *’high-land’, *’rising land’? But see also Early Noldorin oroth ’impetus, haste, speed, rash courage’ (PE13:151), which seems suitable as well – especially considering a people on horsebacks.