Middle Primitive Elvish
rad
root. back, return
grad
root. to flatten, lay low/flat, make flat what was standing
srad
root. to flatten, lay low/flat, make flat what was standing
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.
A root glossed “to flatten, lay low/flat, make flat what was standing” appearing in a list of roots from rejected page in the Quenya Verbal System (QVS) from 1948, with variants and √G)RAD and √SRAD and no derivatives (PE22/127). It appears nowhere else.