Syzygy

1. 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. The coupling together of different feet; as, in Greek verse, an iambic syzygy .
3. 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 immovable union of two joints of a crinoidal arm.
5. The intimately united and apparently fused condition of certain low organisms during conjugation.