noun pl. syzygies -·gies

1. a pair of things, esp. a pair of opposites
2. Astron., Rare either of two opposing points in the orbit of a celestial body, specif. of the moon, at which it is in conjunction with or in opposition to the sun
3. Gr. & Latin Prosody a measure of two feet, as a dipody

Etymology: LL syzygia < Gr < syn-, together + zygon, yoke