wv = "isotope": noun. The prefix iso is obvious and means the same in Greek. Topos as in topography has the meaning of place. The word isotope was coined by a Greek-schooled physician named Margaret Todd to convey the notion of at the same place in the Periodic Table. Thus only chemical species with different numbers of protons get separate seats at the Table. Elements having different numbers of neutrons must share the same seat. This is also true for radioisotopes.
wv = "allotrope": noun: The prefix allo is related to the Greek allos meaning other. Trope is a confusing root and in my opinion is a vague word having several different meanings. The combination allotrope means a structurally different form of the same element ("Graphite and diamond are allotropes of carbon").
Phosphorus and especially sulfur are allotrope-rich. The concept of allotrope is akin to an elemental alias. Sulfur has several different aliases or allotropes. Yes, I like that.