Gnomish
siriol
adjective. flowing, fluent, liquid, mellifluous
Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!
An adjective appearing as G. siriol “flowing, fluent, liquid, mellifluous” in the Gnomish Lexicon, related to G. sîr “river” (GL/67-68).
Neo-Sindarin: I think ᴺS. siriol “flowing, fluent, liquid, mellifluous” can be retained for purposes of Neo-Sindarin, reconceived as an active participle of the later verb [N.] siria- “flow”.