Though also meaning a line drawn on a map connecting points having the same numerical value of some variable, I find a more interesting and entertaining definition of this rarely-used word to be more closely tied to language.
Linguistically speaking, an isogram is a word in which each letter is used only once (as in the case of "subdermatoglyphic"), twice (like "happenchance") and the elusive trio isograms ("deeded", to name one).