an alignment of three celestial objects, as the sun, the earth, and either the moon or a planet: Syzygy in the sun-earth-moon system occurs at the time of full moon and new moon.2.Classical Prosody
. a group or combination of two feet,sometimes restricted to a combination of two feet ofdifferent kinds.3.
any two related things, either alike or opposite.
I mostly know this one from astronomy. Eclipses are a kind of syzygy, as are transits and occultations. The etymology is from the Greek syzygos
(σύζυγος) meaning "yoked together", apparently.