Synonyms for Morganatic (same or very similar meaning)
WordNet sense 1 ((of marriages) of a marriage between one of royal or noble birth and one of lower rank; valid but with the understanding that the rank of the inferior remains unchanged and offspring do not succeed to titles or property of the superior):
left-handedWordNet sense 2 (of marriages and offspring; recognized as lawful):
legitimate, legitimateFrom the ODE community, based on WordNetadd/edit