yúyo noun? adv.? "both" (YŪ, VT48:10). Used adjectivally in yúyo má "both hands"; notice that the noun following yúyo receives no plural or dual marker.
Quenya
yúyo
adjective. both
yúyo
both
atta
cardinal. two
This is the usual Quenya counting number for “two”, derived from √ATATA (VT42/27; VT48/19), which in turn is based on √AT “bi-, double, again (a second time)” (PE17/148, 166). It may be contrasted with yúyo “both” referring to both elements of a pair.
Conceptual Development: There was no word for “two” in the Qenya Lexicon of the 1910s. In the Early Qenya Grammar (EQG) of the 1920s, ᴱQ. yúyo meant “two” and ᴱQ. {satta >>} satto meant “both” (PE14/49, 82). By The Etymologies of the 1930s, these meanings were reversed with ᴹQ. atta “two” appearing under ᴹ√ATTA and ᴹQ. yúyo “both” appearing under ᴹ√YŪ (Ety/ATTA, YŪ).
yu-
prefix. both, both, [ᴱQ.] twice
A prefix for “both” derived from the root √YU of similar meaning (VT48/10; EtyAC/YŪ; PE23/101). It appeared as both yu- and yú-. The short-vowel form seems to be used when it precedes a consonant cluster (yunquë) or a heavy syllable (yucainen), while the long-vowel form is used before a light syllable (yúcale).
In the Early Qenya Grammar (EQG) of the 1920s, ᴱQ. yú was glossed “twice” (PE14/51, 84), because in that document ᴱQ. yúyo was “two” (PE14/50, 82) instead of “both” as it was later. I think as the prefix yu- might still be used for “twice” in Tolkien’s later writings based on words like yunquë “twelve” = “✱twice six” or yucainen “twenty” = “✱twice ten”.
Conceptual Development: There is a prefix ᴱQ. ui- appearing in the Qenya Lexicon as an element in ᴱQ. uiven “twenty” (QL/33) that might be a precursor to yu-. This element is also mentioned in the contemporaneous Gnomish Lexicon along with a variant uivi, but there it was deleted (GL/74).
atta
cardinal. two
atta (1) cardinal "two" (AT(AT), Letters:427, VT42:26, 27, VT48:6, 19). Elen atta "two stars" (VT49:44); notice how a noun is indeclinable before this numeral, and any case endings are "singular" and added to the numeral rather than the noun, e.g. genitive elen atto "of two stars" (VT49:45). Attalyar "Bipeds" (sg. *Attalya) = Petty-dwarves (from Sindarin Tad-dail) (WJ:389). A word atta_ "again" was struck out; see the entry _TAT in Etym and cf. ata in this list.
satto
cardinal. two
satto, "Qenya" numeral "two" (in Tolkiens later Quenya atta) (VT49:54)
mahtanë yúyo má véla
*wielded both hands alike
This is the Quenya word for “both” (VT49/10) derived from √YU of the same meaning (PE17/70). It is likely it can be used as either an adjective or a pronoun: antanes nin yúyo parma “he/she gave me both books” vs. antanes nin yúyo “he/she gave me both”. Yúyo may be contrasted with atta which is the counting word for “two”.
Conceptual Development: The Qenya Lexicon of the 1910s had ᴱQ. aqi “a brace, a couple of, both” as an indeclinable adjective under the early root ᴱ√ATA used for duals (QL/33). In the Early Qenya Grammar (EQG) of the 1920s, ᴱQ. {satta >>} satto meant “both” and ᴱQ. yúyo meant “two” (PE14/82). By The Etymologies of the 1930s, these meanings were reversed with ᴹQ. atta “two” appearing under ᴹ√ATTA and ᴹQ. yúyo “both” appearing under ᴹ√YŪ (Ety/ATTA, YŪ).