The word "illegitimating" is defined as the act of declaring or making something or someone illegitimate. There are various synonyms that can be used instead of "illegitimating". One of the synonyms for "illegitimating" is "disowning", which means to deny any connection with someone or reject something as not being part of oneself. Another synonym for "illegitimating" is "disavowing", which means to deny any responsibility for or support of something. "Annulling" is another synonym that means to declare something as invalid or void. Overall, there are many words that can be used as synonyms for "illegitimating" depending on the context of the sentence.