prime factor noun 1verb 1forms 3 noun1 •A factor of a given integer which is also a prime number.Hence, the prime factors of 100 are 1, 2, 2, 5, 5, and 1 × 2 × 2 × 5 × 5 = 100. From the above illustration, we derive the following rule for finding all the prime factors of any composite number. — 1847 verb1 •To reduce an integer to its set of prime factors.For example, the number 30, which is not prime, can be prime factored as 2 x 3 x 5. — 2008 formsprime factored · prime factoring · prime factors