illegitimate

Short definition from Wiktionary

Adjective

1. 1
   Not conforming to known principles, or established or accepted rules or standards.
2. 2
   Not in accordance with the law.
3. 3
   Not sanctioned by marriage.
4. 4
   Not sanctioned by marriage: Born to unmarried parents.
5. 5
   Not sanctioned by marriage: Having a child or children with a person to whom one is not married.
6. 6
   Not correctly deduced.
7. 7
   Not authorized by good usage; not genuine.
8. 8
   Involving the fertilization of pistils by stamens not of their own length, in heterogonously dimorphic and trimorphic flowers.

Noun

1. 1
   A person born to unmarried parents.

Verb

1. 1
   To make illegitimate.