Is - 10x^8 a monomial.?

-10x^8 is indeed a monomial, because there is only one term. There is nothing else added or subtracted.

There are three types of "nomials":

Monomials: such as the one you have, they only have one term

Example: y, 6x^2, 19084v^22341

Binomials: Equations with two terms

Example: x+1, v+4w, k+1021s

Polynomials: Equation with more than three terms (no limit)

Example: x+5+9z, t+9u+8v

Yep! because there is no +,-, ect. sign. in total it is just one number