born of parents who are not married to each other; born out of wedlock

an illegitimate child.

not legitimate; not sanctioned by law or custom.

unlawful; illegal

an illegitimate action.

irregular; not in good usage.

Logic . not in accordance with the principles of valid inference.

Obsolete . (formerly, in London)

of or pertaining to stage plays in which musical numbers were inserted because of laws that gave only a few theaters the exclusive right to produce straight dramas.

acting in or producing such productions.

a person recognized or looked upon as illegitimate.

to declare illegitimate.