A verb appearing as its Noldorin-style infinitive form tammo “to knock” in The Etymologies of the 1930s, derived from primitive ᴹ✶tambā́- under the root ᴹ√TAM “knock” (Ety/TAM; EtyAC/TAM). In The Etymologies as published in The Lost Road Christopher Tolkien gave the infinitive form as tamno (LR/390), but Carl Hostetter and Patrick Wynne corrected this to tammo in their Addenda and Corrigenda to the Etymologies (VT46/17).
Noldorin
gartha-
verb. to defend, keep
tamma-
verb. to knock
dangen
noun. slain
dangen
adjective. slain
gar-
verb. to hold, have
gerin
verb. I hold, I have
gwedh-
verb. to bind
tir-
verb. to watch
tiria-
verb. to watch
There was a deleted verb N. gartho “defend, keep” in The Etymologies of the 1930s based on the root ᴹ√GARAT, an extension of ᴹ√GAR “keep, maintain, defend” (EtyAC/GAR).
Neo-Sindarin: I think it is worth restoring ᴺS. gartha- “to defend” for purposes of Neo-Sindarin, but for “keep” I would use better known S. heb-.
Conceptual Development: This verb had other meanings in Tolkien’s earlier writings. In the Gnomish Lexicon of the 1910s it was G. gartha- “admire, have affection or respect for” based on the early root ᴱ√gṛþ- (GL/42). The Early Noldorin Dictionary of the 1920s had ᴱN. gartha- “to set, put in position, appoint” (PE13/161), perhaps related to the early root ᴱ√ƷARA “spread, wide places” given the noun ᴱN. garth “place” from the same page in this document.