Traditionally gazpacho was a cold or hot soup made of crushed garlic (and other available veggies), olive oil, vinegar, bread, water. The preponderance of tomato is recent, dating from the 19th century.
According to Joan Coromines (Diccionario crítico etimológico castellano e hispánico, s.v. caspa
), it is probably a Mozarab (i.e. Romance from southern Spain) derivation of a -probably pre-Latin- caspa:
CASPA, origen desconocido, probablemente prerromano y emparentado con otros vocablos como el ast. caspia ‘orujo de la manzana’, sic. caspu y otras formas dialectales del S. y N. de Italia con el significado de ‘orujo de uva’, y aun acaso con oc. gaspo, fr. ant. y dial. gaspaille, que designan residuos diversos de la leche o de los cereales.
In Galician we have a gaspallo
'chaff; trash; dregs' which is identical to the French gaspaille
(equal origin or perhaps a Medieval borrowing Old French -> Galician). Also we have the related gaspallar
'to mince; to destroy'; gaspallada
'fragments of vegetation, brushwood, etc.'; gaspelleiro
'broken field'... Gaspallo itself is used by Cernadas y Castro
, a 18th century author, as synonym of gazpacho, in a poetic competition full of double meanings. It's use is probably intentional, comparing food/a poetic composition with dregs/trash, but still they are probably related words:
Non fagas Copras mordentes,
que no teu frio gaspallo,
ben conocemos ó Allo,
sin que nos mostres os dentes:
son moytos os ingredentes,
de que se fay unha ola,
é anque na tua Cachola,
ó Allo porreta bóte,
ben sabes que en qualquer póte
ay do Allo, ay da Cebola.
"Don't compose mordant couplets
because in your cold ''gaspallo
we have already meet the garlic,
without you showing the cloves to us [= without showing your teeth]:
there are many ingredients
to make a pot,
and although in your little pot [= in your head]
the garlic is shooting a bud,
you know well that in any pot,
there is garlic, there is onion [Woe!
: "ay de" woe!; "hai" is]
The French word, and hence the Galician ones, could
have ultimately a Germanic origin (gaspiller - Wiktionary
), although Coromines favoured a pre-Latin one for this family.