In his detailed but unfinished index to The Lord of the Rings, Tolkien interpreted the name Kibil-nâla as 'silver-channel'. In later notes he makes it clear that the meaning of Dwarvish nâla is not specifically known, but on the assumption that the meaning of Kibil-nâla mirrors Elvish Celebrant or Mannish Silverlode, then kibil would mean 'silver', and nâla would mean 'channel' or 'course'.
It might be noted that the Dwarvish mountain name Zirakzigil ('Silvertine') also contains an element meaning 'silver'. Evidently, as Tolkien himself observed, the Dwarves had more than one word with that meaning. He further suggested that in the case of Zirakzigil, the relevant name-element perhaps referred to the silver-grey colour of the mountain, rather than literally to the metal, traces of which were indeed to be found in the river named Kibil-nâla.
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