-oid's a suffix much used in the sciences and mathematics to indicate a "similarity, not necessarily exact, to something else". According to the Oxford English Dictionary, -oid's derived from the Latin suffix -oides taken from Greek and meaning "having the likeness of". Thus, asteroid means "like a star" and rhomboid means "like a rhombus". There're many examples of such words: android, anthropoid, alkaloid, factoid, humanoid, planetoid, trapezoid and so forth. When nouns formed using -oid are… (More on -oid)