The Quenya word for “double” in notes from the late 1960s derived from primitive ✶atatya, an adjective form of the root √ATATA (VT42/26-27).
Conceptual Development: The Etymologies of the 1930s had ᴹQ. tanta “double” under the root ᴹ√TATA “two” (Ety/TATA) and ᴹQ. atwa “double” under the root ᴹ√AT(AT) “again, back” (Ety/AT(AT)). The latter was glossed “either ... or” in Demonstrative, Relative, and Correlative Stems (DRC) from 1948 (PE23/107); see the entry for ᴹQ. atwa for further discussion.
atatya vb? adj.? "double" (VT42:26)