Sentence:  A Discovrse concerning a New <WSD>Planet</WSD>. Tending to prove, That 'tis probable our Earth is one of the <WSD>Planets</WSD> 
Meaning of the word marked with <WSD> tags:  A body which orbits the Sun directly and is massive enough to be in hydrostatic equilibrium (effectively meaning a spheroid) and to dominate its orbit; specifically, the eight major bodies of Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. (Pluto was considered a planet until 2006 and has now been reclassified as a dwarf planet.) (from 17thc.)