The basis for Elvish “tree” words, this root first appeared in The Etymologies of the 1930s as an extension of ᴹ√GALA “thrive” (Ety/GALAD). This replaced the earliest derivation of “tree” from the Qenya Lexicon of the 1910s, where the Qenya word for “tree” ᴱQ. alda was derived from ᴱ√ALA “spread” (QL/29). In The Etymologies, the Quenya form of this word remained the same, but the 1910s Gnomish words G. âl “wood” and †alwen “tree” (GL/19) became the 1930s Noldorin word N. galadh “tree” (Ety/GALA). Quenya and Sindarin retained these words for “tree” thereafter, and while Tolkien did not mention the root √GALAD again, his continued use of primitive ✶galadā “tree” (Let/426; PE17/153; PE21/74; UT/266) made it clear this root remained valid.
Middle Primitive Elvish
tōp-
verb. to roof
top
root. cover, roof, roof, cover
galad
root. tree
galadā
noun. tree
kas
root. head
kas
noun. head
kast
adverb. towards the top
khar
root. helmet
kharan
root. helmet
kharap
root. helmet
A root in The Etymologies of the 1930s glossed “cover, roof” with derivatives like ᴹQ. tópa-/N. toba- “to roof”, ᴹQ. tópa “roof”, and N. tobas “roofing” (Ety/TOP). It was grouped together with and was apparently a variant of ᴹ√TUP (EtyAC/TOP), a root with a much lengthier history; see that entry for details. For purposes of Neo-Eldarin, I think this root could mean “roof” as opposed to √TUP = “cover”.