No. The Fisher (Martes pennanti), also sometimes referred to as a fisher cat, is not a feline at all, it is actually part of the weasel family. The Fisher shares the same Genus with Martins such as the Pine Martin and American Martin.
This is from wikipedia: The term big cat - which is not a biological classification - is used informally to distinguish the larger cat species from smaller ones. One definition of "big cat" includes...
Most people think the lion, but in fact it is the tiger which weighs more and is stronger. -- actually, the tiger would be the strongest "cat" you find in the wild. Otherwise, tiglons (hybrid, tiger...