IPA: /ˌɪlɪˈdʒɪtəməsi/
KK: /ɪlɪˈdʒɪtəməsi/
The state of being born to parents who are not married to each other, or the condition of being not allowed by law or rules.
The illegitimacy of the contract was questioned in court.
Illegitimacy is formed from "il-" (meaning not), "legitimus" (meaning lawful or legitimate), and "-acy" (meaning the state or quality of). The word refers to the state of being not lawful or not legitimate.
Think of 'not' ('il-') and 'lawful' ('legitimus') to remember that 'illegitimacy' means the state of being not lawful.