The prefix post- means “after,” and the Latin word humus means “ground.” Add the suffix -ly and that lets you use the word to describe some action taken after someone’s dead and in the ground, like posthumously naming a street after a dead politician, or posthumously publishing a new book written by an author who died years ago. The word doesn’t sound how it looks, so pronounce it like this: POSS-chew-muss-lee.