I would suggest you begin here:
Slide down to variants and dialects. I'm afraid there is no one source for finding the variants of vocabulary, unless it's a good dictionary. Think of English and the regional differences. In Spanish (or Castellano) there is Peninsular Spanish, Latin American Spanish with each country/regiion having its own pecularities.
For example, the word "bus" could be: autobús, camión or even guagua. Now, take the word "guagua" because it could be a trifle/a trivial thing, an insect in Cuba and Mexico, a baby in Argentina, Bolivia, Chile, Ecuador, Peru, an omnibus/streetcar in Cuba.
Take the word "car" which could be all of the following, depending upon where you are: carro, carreta; vagón ; coche, automóvil. You are in for fun doing this assignment!
P.S. I just had to come back to see how you were doing! Having had native speakers from different countries, this is most interesting to me! I remember one year with a girl from la Argentina, a boy from Spain (las Provincias Vascongadas) and another boy from Puerto Rico in the same class and when the rest of my students couldn't understand why they couldn't understand each other!
Some other examples that come to mind:
cake: torta, biscocho (Caribbean), but it's a "roll" in Latin America and queque from Central America.
boy: chico, muchacho, mozo, compadre (more like slang), even vato (Chicano)
corner store: el chino (Panama), el colmado (Caribbean), la bodega (Cuba) la pulperia (Nicaragua)
soda = gaseosa (el Perú), refresco (Dominican Republic but in el Perú "refresco" is a sweetened drink or punch. (and even "el ponche" from some Chicanos)
blond(e): rubio (-a)(Spain), blondo (-a), fulo (Panamá), huero (-a), (México)
pig = puerco, cedo, cochino
peach - melocotón, durazno
avocado = aguacate (México), paldad (SA), even "avocado"
kite = papalote (México), barrilete (la Argentina), cometa
When it comes to the "ultimate authority" it is, of course, La Real Academia Española.
thank you so much; I have not been able to complete the assignment yet, but the information you have provided has been wonderful.
thank you so much; I have not been able to complete the assignment yet, but the information you have provided will be extremely helpful!
sorry computer malfunction