- 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.
- a group or combination of two feet, sometimes restricted to a combination of two feet of different kinds.
- any two related things, either alike or opposite.
- either of the two positions (conjunction or opposition) of a celestial body when sun, earth, and the body lie in a straight line
- (in classical prosody) a metrical unit of two feet
- any pair, usually of opposites
- the aggregation in a mass of certain protozoans, esp when occurring before sexual reproduction
