Syzygy

n.	1.	(Astron.) The point of an orbit, as of the moon or a planet, at which it is in conjunction or opposition; - commonly used in the plural.
	2.	(Gr. & L. Pros.) The coupling together of different feet; as, in Greek verse, an iambic syzygy.
	3.	(Zool.) Any one of the segments of an arm of a crinoid composed of two joints so closely united that the line of union is obliterated on the outer, though visible on the inner, side.
	4.	The intimately united and apparently fused condition of certain low organisms during conjugation. Line of syzygies (Astron.) the straight line connecting the earth, the sun, and the moon or a planet, when the latter is in conjunction or opposition; - used chiefly of the moon.

Noun

1.

syzygy - the straight line configuration of 3 celestial bodies (as the sun and earth and moon) in a gravitational system

physical phenomenon