The usual word for “and” in the 1910s was ᴱQ. ya(n) (PE15/69, VT40/8). It was derived from the early root ᴱ√YA (or possibly ᴱ√(D)YṆTṆ) in the Qenya Lexicon of the 1910s (QL/104-105). In his later writings, the usual word for “and” was Q. ar, but something like ya(n) survived in the “dual” conjunction yo “both ... and”.
Early Quenya
yan
conjunction. when
yanta
adjective. joined
ya(n)
conjunction. and
yanda
adjective. dark, gloomy
An adjective in the Qenya Lexicon of the 1910s glossed “dark, gloomy”, a derivative of the early root ᴱ√YAÐA (QL/105).
yando
adverb. also
yanta
adjective. large
yanta-
verb. to add to, enlarge, increase, augment
ya
pronoun. relative pronoun
yantya-
verb. to add to, augment
yanwa
noun. goose
yar i vilya anta miqilis
to whom the air gives kisses
-víke
suffix. as
anta-
verb. to give
ne
conjunction. that
penda
noun. bridge
sanda
adjective. that
santo
pronoun. that
tanya
adjective. that
yalta
noun. yoke
yalte
noun. yoke
yarta
noun. yoke
yáme
adjective. yawning
úmea
adjective. large
An adjective appearing in Early Qenya Word-lists of the 1920s as ᴱQ. yanta “joined” (PE16/142) likely based on the early root ᴱ√ẎATA “join” (QL/105).
Neo-Quenya: For purposes of Neo-Quenya, I would update this to ᴺQ. yantaina “joined” as a passive participle of ᴺQ. yanta- “to join”.