The term 'Amnion' is a four-letter word that can be found in crossword puzzles. It is an anatomical term referring to the innermost membrane of the amniotic sac, which is a fluid-filled sac that surrounds and protects a developing embryo in the uterus. The related term 'Caul' is also a four-letter word that can be found in crosswords. It refers to the amniotic membrane that sometimes covers the head and face of a newborn baby at birth.