Imagine you're dealing with a formula which has a special type of variable in it. This variable is specified at the outset as being not equal to zero, which is good, because you need to divide by it as part of using the formula. However, the variable does get arbitrarily close to zero. In fact, you're pretty much taking the limit as it goes to zero. And at the end of this, when you get a result that involves this variable, you'll want to treat it as though it's equal to zero so that you can cancel out some terms. But despite this, the variable is by definition nonzero.
So the variable has an interesting and complex relationship with zero, and it's important not to add in any more confusion regarding this. Bearing all that in mind, what letter would you use to denote the variable?
If you said "the letter O," you have what it takes to be an 18th-century mathematician.