An Etymological Dictionary of Astronomy and Astrophysics

The alignment of three or more celestial bodies in the same gravitational system along a nearly straight line.
Conjunction or opposition of a heavenly body with the Sun.

Etymology (EN): From L.L. syzygia, from Gk. syzygia “yoke, pair, union of two, conjunction,” from syzygein “to yoke together,” from → syn- “together” + zygon “yoke,” cognate with Pers. yuq, jug “yoke,” as below.

Etymology (PE): Yujân from yuj “yoke,” variants yuq, juh (Mid.Pers. jug, ayoxtan “to join, yoke;” Av. yaog- “to yoke, put to; to join, unite;” cf.
Skt. yugam “yoke;” Hittite yugan “yoke;” Gk. zygon “yoke,” as above, zeugnyanai “to join, unite;” L. jungere “to join,”
O.C.S. igo, O.Welsh iou, Lith. jungas O.E. geoc. PIE base *yeug- “to join”) + -ân suffix of place and time.