The formal scientific definition of theory is quite different from the everyday meaning of the word. (religion.blogs.cnn.com)
Historically, there had been no formal scientific definition of «planet» and without one, the solar system had been considered to have various planets over the years. (newworldencyclopedia.org)
But it's also pretty darn close to this word's most common scientific definition: when one astronomical object aligns with another. (discovermagazine.com)