The invitation was one which, a year earlier, would have provoked a less ready response, for the party, though organized by Mrs. Fisher, was ostensibly given by a lady of obscure origin and indomitable social ambitions, whose acquaintance Lily had hitherto avoided.
There are no more uses of "indomitable" in the book.
Show samples from other sources
She is remembered for her indomitable spirit.
And that the great monster is indomitable, you will yet have reason to know.