1. [n]  a mathematical expression that is the sum of a number of terms
2. [adj]  having the character of a polynomial; "a polynomial expression"

POLYNOMIAL is a 10 letter word that starts with P.

1. \Pol`y*no"mi*al\, n. [Poly- + -nomial, as in
   monomial, binomial: cf. F. polyn[^o]me.] (Alg.)
   An expression composed of two or more terms, connected by the
   signs plus or minus; as, a^{2} - 2ab + b^{2}.
   
   

2. \Pol`y*no"mi*al\, a.
   1. Containing many names or terms; multinominal; as, the
      polynomial theorem.
   
   2. Consisting of two or more words; having names consisting
      of two or more words; as, a polynomial name; polynomial
      nomenclature.
   
   

1. An arithmetic expression composed by summing multiples of powers of some variable.

        P(x) = sum a_i x^i for i = 0 .. N

The multipliers, a_i, are known as "coefficients" and N, the highest power of x with a non-zero coefficient, is known as the "degree" of the polynomial. If N=0 then P(x) is constant, if N=1, P(x) is linear in x. N=2 gives a "quadratic" and N=3, a "cubic".

2. polynomial-time.