Sindarin 

-ion

suffix. regional ending

_ suff. _regional ending. In older names, it usually applied only to a single feature (e.g.Sirion 'the Great Stream'). It was esp. applied to topographical features of large extent, esp. long, wide river, long (and wide) ranges. It was mostly used in post-Exilic times and so was probably partly due to Quenya influences. >> -on, Eregion, Nanduhirion, Sirion

Sindarin [(PE17 Sindarin Corpus) PE17:37:42-3] < S. _iaun_ large, extensive, wide < _ı_9_aun_ < _yānā_ < YANA < _yā- _wide, large, extensive. Group: Parma Eldalamberon 17 Sindarin Corpus. Published by