§ Tarkilmar >> Torfirion ’Westermanton’ (TI:144-145)
These are earlier names of Annúminas, the capital of Arnor.
The former variant is clearly Quenya containing attested Tarkil (pl. Tarkildi) ’Great Men of Númenor’, in other notes tarkil(di) ’high-men = Elf-friends of Númenor’ (VT46:17, TĀ-,TAƷ-; KHIL-) and -mar ’home’ (MBAR-, PE17:104-109), appearing in many place-names.
The latter variant seems to be a translation into Noldorin, torfir being the cognate of tarkil (ibid., PHIR-). The suffix -ion is then either name-formative with i-reduplication from the stem, adjectival or denoting a region, see the note 4.4 at the end.