An adjective in the Gnomish Lexicon of the 1910s glossed “stealthy” based on G. nig- “steal, creep, do or go by stealth” (GL/60).

Neo-Sindarin: I don’t recommend using the verb G. nig- “steal, creep”, since in Tolkien’s later writings the root √NIK means “small”. However, I do retain the Gnomish noun G. nig(la) “mouse” adapted as ᴺS. nigol = “small one”, so I retain and adapt this Gnomish adjective as ᴺS. nigren, originally meaning “mouse-like”.