The crossword solution for the term LEAD-IN TO SKELETON is EXO. EXO is a three-letter word that is used to refer to the external part of an organism or structure, which is the lead-in to the skeleton. It is derived from the Greek word 'exo, ' meaning 'OUTSIDE.' In anatomy, exo refers to the outermost layer of the body, such as the skin, and in architecture, it refers to the outermost layer of a building, such as the walls.