"old Tom"

Thank you very much for your answers, ESC and Steve!

Another question if you please (connected to the previous):

"Some friends of mine had a cat, a big black Tom...One day a Chinchilla came to live in the neighbourhood and the two cats met at a garden wall party."

Do you think that Tom and Chinchilla are their names or perhaps Tom stands for a "male cat" also(as "old Tom" does)?

"Tom" means an unneutered male cat. A dictionary would have answered that question for you. In cats, "chinchilla" refers to a silvery-white coat color.