The Greek philosopher Aristotle thought of comets as dry exhalations of the Earth, planet, and stars, that caught fire high in the atmosphere.

Comet comes from the Greek word κομήτης, or komētēs, which translates to “long haired (star)” in English. 

They were sighted long before they were named, before the 12th century, and were thought of as bad omens foreshadowing wars, famine, death and family, which often occurred shortly after their sighting. 

Today, Merriam Webster understands the comet as a celestial body that looks like a fuzzy head usually surrounding a bright nucleus with a highly eccentric orbit of ice and dust, developing into one or more long tails when near the sun.