Mumps is ‘an acute, inflammatory, contagious disease caused by a paramyxovirus and characterized by swelling of the salivary glands, especially the parotids, and sometimes of the pancreas, ovaries, or testes’ (AHD). The disease affects mostly children and it causes a painful swelling of the neck. The symptoms of this highly contagious disease arise a couple of weeks after exposure to the virus and disappear in a week to ten days. Symptoms are more severe in adults but one third of those infected show no symptoms. Complications of mumps include meningitis (15%), among other possibilities. There is currently a mumps vaccine, which is typically administered in combination with vaccines for measles, rubella, and varicella. The name for this disease in Spanish is paperas.
The word mumps was originally the plural of mump [ˈmʌmp], a word that meant ‘a grimace, a moue; an exaggerated facial expression’ and it was ‘probably an imitative or expressive formation’ (OED), that is, ‘symbolic of the movements of the mouth in grimacing’ (SOED). This meaning of the word is now obsolete. The word first appears in the late 16th century, first as a verb, meaning ‘to grimace’, a sense that is now obsolete, though this verb is still used dialectally in England with different senses, such as ‘to grimace with the mouth : grin’, ‘mumble’, and ‘to be sullen or sulky’ (WNTIU). The plural form mumps for the disease, as in to have the mumps, is analogous to other plurals of this sort, such as in have the giggles or have the sniffles.
The word paperas is already attested in the 15th century for this disease. It would seem to be ultimately derived from the word papo that refers to the bulging part between the chin and the neck (double chin in people and dewlap or crop in animals) and, by extension it can also mean ‘jowl’, which can also be used figuratively (synonym: desfachatez ‘audacity, nerve’). (The word sopapo ‘slap, smack’ is derived from papo with the prefix so‑ derived from Lat. sŭb ‘under’.)
The word papo is itself derived from the archaic Spanish word papa that meant ‘soft food’, derived from Lat. pappa, a children’s word for food’. More common today is the diminutive papilla ‘baby food, pap, mush, puree (for sick people)’ (Eng. pap is a cognate; derived from the noun there was the verb papar ‘to eat’, which is now obsolete). This word papa is a homophone of the word papa that means ‘pope’ and ‘dad’ (the latter also papá, though French influence), through Lat. pāpa or pappa, from Gk. πάπας (pápas) ‘bishop, patriarch’, a variant of πάππας (páppas) ‘father’. This Spanish word papa is also a homophone of the word papa that means ‘potato’, which comes from Quechua papa.
The actual form of the word paperas and, in particular its suffix ‑eras, must be due to it having been derived from the word papero derived from papa, synonym of the plural papas ‘soft baby food’, as well as of the pot where the food was made.