Perhaps related to Khuzdul kibil "silver"
Adûnaic
gimil
collective noun. (all) stars; ?silver
Khuzdûl
gimil
gimil
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!
Primitive adûnaic
gimil
root. *star
One of the roots Tolkien used to illustrate various processes of Primitive Adûnaic word formation (SD/422-5). It also seems to be the basis of words related to stars, such as gimli.
A collective-noun meaning “all the stars of the heavens”, as opposed to gimli which was used for an individual star (SD/427). The element gimil appears in many names, including several later names in The Lord of the Rings and The Silmarillion. Carl Hostetter and Patrick Wynne suggested (AAD/15) that it may be related to the Elvish root √(Ñ)GIL “shine (white)”.
Andreas Moehn suggested (EotAL/KH-B-L) that if the later name Gimilzôr means “Silver-fire”, its initial element gimil could instead mean “silver”, perhaps as a cognate of Dwarvish kibil. If so, this alternate meaning could either be a homonym of gimil “stars”, or a new meaning for gimil in Tolkien’s later works.