Uilos is one of two Elvish names given to the flower referred to by Men as simbelmynë ("Evermind"). This name was used for the flowers that Tuor found growing around the Gate of Silver on the journey into Gondolin, and is not recorded after the end of the First Age. Texts referring to the Third Age seem to prefer the Elvish name alfirin for the same white, star-like flower, but whether this signals a change of name across the ages is not known.
The Sindarin word uilos is not literally equivalent to "Evermind", but rather has a meaning closer to "Everwhite". The "Ever-" element in both these names alludes to the fact that the flowers didn't have a particular season, but instead appeared throughout the entire year.