An old friend of mine recently asked that question.  It's a deceptively tricky question, the longer one thinks about it, especially in the Copy Room of Revelations.  It gets sticky of course, because everything does.  The spiritual part gets dicey, because you could totally be a Witch and still identify as a Major Religion and go to a Major Religion Service regularly and still practice some version of Witchcraft.  Hoodoo (Southern North-American folk magic) is literally built on this.  There are no Hoodoo gods.  You talk to the gods you came with, who are probably some kind of Christian.  You might talk to saints and spirits.  But Hoodoo does not have [Goddess Name], the goddess of [Action X].   It is an add on to your American-Christian Starter Pack, though people who don't identify as American-Christian use it too as we are all more shameless versions of The Borrowers in matters of the Craft. 

Conversely, you can identify as a Witch and choose to worship only the (Wiccan) God & Goddess pair, the (Dianic WIccan) Goddess and/or a mish mosh pantheon of polytheistic goddesses from various places in the world, some of whom mostly went to sleep for a while (Greek pantheon, Roman patheon, Celtic pantheon, etc) and some of whom never went to sleep (the Hindu pantheon, some fae in Nordic/Celtic countries, the Buddhist pantheon). 

The spiritual aspect is very electic for Witches, I find.  There's also Witches who are into Animism, Agnosticism, Gnosticism and Ancestor worship and any combination you can think of.  Atheist Witches too.  

Gender isn't really an issue either.  Boys, girls, non-binary gender people all identify as witches in this day and age.  And why not?  If we were busily burning, hanging and crushing people for whatever was considered Witchcraft of the day, it seems egalitarian to make it open for everyone to come on down.

So what does that leave if we've sort of side stepped spirituality?

It leaves Witchcraft. 

Here's where it gets sticky again, because really, what's Witchcraft?  It's magic, but what's that?  The phrase "the magic of prayer" is often used in lots of spiritual practices.

An inconclusive list:

prayer

performing healing magic

performing hexing magic

setting an intention

glamour

energy work

meditation

trance work

performing a ritual

performing ritual worship

performing magic on yourself

performing magic on others

magic that involves components such as crystals, herbs and blood

magic that does not require any components

magic that requires incantation

magic that does not require incantation

magic that you follow from a book

magic that you make up yourself

So as you can see, it gets to be very gray.  Some argue that a Witch needs to be able to heal and hex, some don't feel that's necessary.  I think about a conversation I had with my mom years ago, when she was being dismissive of magic being "real".  I sighed in annoyance and said, okay fine.  Then what exactly are you doing when you buried a statue of St. Anthony upside down in your yard and would not unbury him until you sold the house?  What's that?  Where's that "how to" in the New Testament?  It worked, didn't it?  It worked because you set your intention and followed a folkloric recipe . . .also known as  magic.  So, that ended that line of questioning, because let's face it, Catholicism is riddled with magic which is why Protestants wanted a break from it.  But Protestants are (less obviously, but still) riddled with magic, too.  That's why the Salem Witch trials happened, because plenty of Puritans were practicing magic.  Telling the future with egg yolks, using a colander like a Ouija board, poppet making and other fun things that everyone pretended they weren't usually doing together.

I identify as a Witch because:

• I have an eclectic pantheon of spirits, ancestors and goddesses that I worship, including bits from my Catholic roots
• I perform WItchcraft for healing myself and others, for hexing and to obtain things I Want in this life along with trance work and ritual work (both alone and in groups)

Simply, a Witch is someone who practices Witchcraft.  Do you think you practice magic?  Then you're a Witch.  Do you feel your spiritual practice is sans Witchcraft?  Then you're not a Witch.