illegitimate

nouns

the illegitimate offspring of unmarried parents
bastard, by-blow, illegitimate, illegitimate child, love child, whoreson

adjectives

contrary to or forbidden by law
"an illegitimate seizure of power"; "illicit trade"; "an outlaw strike"; "unlawful measures"
illegitimate, illicit, outlaw, outlawed, unlawful
of marriages and offspring; not recognized as lawful
illegitimate
antonym
legitimate
is similar to
conceived in adultery
adulterine
is similar to
illegitimate
base, baseborn
is similar to
born out of wedlock
"the dominions of both rulers passed away to their spurious or doubtful offspring"- E.A.Freeman
bastardly, misbegot, misbegotten, spurious
is similar to
not having a known or legally responsible father
fatherless
is similar to
(of marriages) illicit or informal
"in Colonial America left-handed marriages between Frenchmen and Indians were frequent"
left-handed
is similar to
having no legally established claim
"the wrongful heir to the throne"
unlawful, wrongful
see also
not endowed with authority
unauthorised, unauthorized
see also
prohibited by law or by official or accepted rules
"an illegal chess move"
illegal
see also
having no cogency or legal force
"invalid reasoning"; "an invalid driver's license"
invalid