A hypothetical early root explaining the words in the Gnomish Lexicon of the 1910s such as G. huir “foggy” and G. huith “fog” (GL/49). It may have been a variant of ᴱ√ǶUẎU “*night” (QL/41).
Related
?HUYU “*fog” may be a (Gnomish only?) variant of ǶUẎU “*darkness”