Middle Primitive Elvish
ros
root. *plain
ros
root. distil, drip
phal
root. foam
There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
An unglossed root in The Etymologies of the 1930s with the derivative Ilk. rost “plain, wide land between mountains”, an element in the names Ilk. Nivrost “West Vale” and Ilk. Radhrost “East Vale” (Ety/ROS²). In later versions of The Silmarillion these names became S. Nevrast “Hither Shore” (S/119) and S. Talath Rhúnen “East Vale” (S/124), making it likely that ᴹ√ROS “✱plain” was abandoned.