The word guacamole was borrowed from Spanish in the early twentieth century, and they took that from the Aztecs and their word ahuacamolli. That's a portmanteau of ahuacatl, meaning "avocado", and molli, meaning "sauce" (this is also the etymon of the Mexican sauce mole). Makes a lot of sense. I've already covered ahuactl before, but it had a curious secondary definition of "testicle", due to visual resemblance. The eventual root is thought to be Proto-Aztecan pawa, also referring to the fruit. Molli, meanwhile, probably took a similar route but we don't have a reconstruction for it. The shortening guac (which is largely limited to North American colloquial speech) was spawned in the early 1980s, and the expression holy guacamole modified the pre-existing holy moley, which has been around since the 1940s and referred to a magical herb from Greek mythology.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.