A noun for “leap” appearing in names like Cabed Naeramarth “Leap of Dreadful Doom” and Cabed-en-Aras “Deer’s Leap” (S/224; UT/150), apparently the gerund of a verb cab- “leap, ✱jump” based on the root ᴹ√KAP of similar meaning.
Conceptual Development: This root dates all the way back to the Gnomish Lexicon of the 1910s, and there are similar nouns based on this root appear in Tolkien’s earlier writings: G. camp “leap” in the Gnomish Lexicon of the 1910s (GL/24) and ᴱN. cais “leap” in Early Noldorin Word-lists of the 1920s (PE13/140). The latter was based on primitive ᴱ✶kapse, with the diphthong ai the result of the vocalization of p to i.
A verb for “to leap” implied by the noun [gerund] cabed “leap” in names like Cabed Naeramarth “Leap of Dreadful Doom” and Cabed-en-Aras “Deer’s Leap” (S/224; UT/150).
Conceptual Development: This verb dates all the way back to the Gnomish Lexicon of the 1910s, which had G. cab- “jump, leap” (GL/24) clearly based on the early root ᴱ√KAPA “leap, spring” from the contemporaneous Qenya Lexicon (QL/45). The Early Qenya Phonology had ᴱN. hab- “to jump” based on a variant root ᴱ✶skap- (PE14/66), but at some point after this cab- was restored, as implied by N. cabor “frog = ✱leaper” from The Etymologies of the 1930s (Ety/KAP).