Is nihilism the same as depression?

Answer 1

I guess, in a sense, but not really.

Nihilists do not believe the organizational values of society have any true value so they are inclined to disassemble them. Nietzsche characterized nihilism as emptying the world and especially human existence of meaning, purpose, comprehensible truth, or essential value.

One could argue that a sense of dispair can emerge from a belief in nihilism. Dispair, I believe, is a subset of depression.

Answer 2

Nihilism is a system of thought, in which the person makes a conscious decision to believe in nothing. The American Heritage Dictionary defines it as "an extreme form of skepticism that denies all existence.
A doctrine holding that all values are baseless and that nothing can be known or communicated." Depression is a medical condition.

Answer 3

I think that is true for many people. We all have a philosophy of living whether we formalize it or not. We can say, for example, that we believe in God but then live our lives without reference to God - that would make us functional atheists.

To be a functional nihilist all we have to do is to think about the consequences of rejecting God. With that rejection comes the rejection of purpose and with purpose goes meaning and with meaning goes worth.

“Unless you assume a God, the question of life’s purpose is meaningless.” –Bertrand Russell

"There is only one really serious philosophical question, and that is suicide. Deciding whether or not life is worth living is to answer the fundamental question in philosophy. All other questions follow from that." -- Albert Camus

Honest atheism always leads to nihilism and honest nihilism leads to suicide.