Definition of monomial I thought the definition of a monomial is an algebraic term that has no subtraction or addition. I saw on my online college homework that 2/x is not a monomial. Why?
As @Fundamental pointed out in a comment, your definition of monomial is wrong. See Wikipedia for a better definition.

Or here is a simpler definition. A monomial is a constant, a variable, or the product of constants and/or variables.

Details: The monomial is usually simplified to place the constant, if any, first, and to combine multiple copies of the same variable into a positive integral power of the variable. The variables are also usually written in alphabetical order.

Your expression $2/x$ does not meet my definition or Wikipedia's, so it is not a monomial.
As @Fundamental pointed out in a comment, your definition of monomial is wrong. See Wikipedia for a better definition.

Or here is a simpler definition. A monomial is a constant, a variable, or the product of constants and/or variables.

Details: The monomial is usually simplified to place the constant, if any, first, and to combine multiple copies of the same variable into a positive integral power of the variable. The variables are also usually written in alphabetical order.

Your expression $2/x$ does not meet my definition or Wikipedia's, so it is not a monomial.