§ {Tar} Arad Dain – probably ’High Pass’ (RS:416,432)
Christopher Tolkien writes:
I do not understand the reference of ’Arad Dain (Annerchin)’. My father first wrote Tar and struck it out before writing Arad.
But with Tar Tolkien seems to have begun a word meaning ’high’ – see TĀ-, TAƷ- ’high, lofty, noble’ and its derivatives; the names of the kings of Númenor mostly start with Tar- ’high’; compare also Tarkilmar ’Westermanton’ and Tar as an early name of Celeborn below (2.34). This is however, Quenya – Noldorin has forms with a long ā, later diphthongized to au > o. But a root TAR- is cross-linked under ƷARA- (VT45:17) and TUR- (VT46:20) in The Etymologies, although it does not appear as an entry. So it seems likely that Arad Dain refers to the ’High Pass’ on page 416.
If so, arad may have two explanations – it may be the adjective ’high’ (compare later ARA- ’noble’, arātā > S. arod (PM:363)). Or it could be a derivative of RAT- ’walk’ (whence N. râd ’path, track’) with prefixed sundóma meaning ’pass’.
According to this, dain should then mean ’pass’ in the former case and ’high’ in the latter, and is perhaps lenited. The stems TAN- ’make, fashion’ and (N)DAN- ’back’ do not suit the meaning, but DEN- ’hole; gap, passage’ with the derivative N. dîn ’opening, gap, pass in mountains’ seems to do. Thus one could explain dain by the sound change *denjā > *dein > dain *’pass’. The suffix -jā is common in forming adjectives, but compare also Q. kirya, N. ceir ’ship’ (KIR-) or Q. ranya, S. rein, rain ’erratic wandering’ (VT42:13) from primitive *kirjā, *ranjā.
However, dain is also directly attested in Early Noldorin as ’high, noble, divine’ (PE13:141), derived from dagná. By the time of The Etymologies we have DAƷ- ’great’ (VT45:8) with daʒrā > N. daur ’great, large’ (which was deleted). According to the phonology of Noldorin as presented in The Etymologies the back spirant ʒ becomes e̯ as part of a diphthong in such a position, cf. maʒiti ’handy, skilled’ > N. moed, but Tolkien wrote later:
Originally the difference between correct Sindarin ae and ai was neglected, ai more usual in English being used for both in the general narrative. (VT42:11)
Arad Dain was put down very early, we do not know how much of The Etymologies was written at that time. In Early Noldorin at least we always see ai as in the very example of dain. Hence, the most probable explanation appears to me: arad *’pass’ and dain ’high’ with the adjective in the usual trailing position and without lenition.