irreducible

Short definition from Wiktionary

Adjective

1. 1
   Not able to be reduced or lessened.
2. 2
   Not able to be brought to a simpler or reduced form.
3. 3
   Unable to be factorized into polynomials of lower degree, as (x² + 1).
4. 4
   Whose numerator and denominator share no common factor greater than 1.
5. 5
   Unable to be factored into smaller integers; prime.
6. 6
   Whose only divisors are units and associates.
7. 7
   Inexpressible as the union of two proper algebraic subvarieties.
8. 8
   Not containing a sphere of codimension 1 that is not the boundary of a ball.
9. 9
   Impossible to divide further into representations of lower dimension by means of any similarity transformation.

Noun

1. 1
   Such a polynomial