An element meaning “foam” (or perhaps “*spray”) in the name Q. Elerossë “Star Foam” cognate of S. Elros in notes from the late 1960s (PM/349), or “rain” in the name of the waterfall Q. Raurossë “Roaring-rain” cognate of S. Rauros in notes probably from the 1950s (PE19/99). A form rosse “rain” appeared in Eldarin Pronouns, Demonstratives, and Correlatives (EP2) from the early 1950s (PE23/123); in context this form seems to be Primitive Eldarin, but it could be Quenya since the expected primitive form would be ✶rossē (Let/282). In The Etymologies of the 1930s, Tolkien gave ᴹQ. rosse “fine rain, dew” as a derivative of the root ᴹ√ROS¹ “distil, drip” (Ety/ROS¹).

Neo-Quenya: For purposes of Neo-Quenya, I would assume this word means a light rain or a continuous spray of water, or the remnants of such water in the form of dew, in other words any persistent collection of small droplets of water either in the air or on the ground, for example from light rain, morning dew or falling mist off a waterfall. This seems to be in keeping with most of its attested glosses.

For more ordinary or heavier rain, I’d use ulo instead, or for a drizzle I’d use mistë, and would reserve rossë only for a light mist-like rain. For a floating mist or fog, I’d use hísë or (if thicker) hiswe. Thus of precipitation, I’d have ulo > mistë > rossë > hísë in decreasing ranks of density, where hísë “mist” is light and/or cold enough not to longer fall. But I think rossë can also refer to “already fallen” droplets in the form of dew.

Raccoon suggested this word may also have the extended meaning “shower”, as posted on 2024-05-03 in the Vinyë Lambengolmor Discord Server (VLDS), including the sense “instance of taking a shower”.