Many also will have participles, infinitives, phrases, and sentences, to be occasionally "in the objective case:" whereas it must be plain to every reader, that they are, all of them, indeclinable terms; and that, if used in any relation common to nouns or pronouns, they assume that office, as participles, as infinitives, as phrases, or as sentences, and not as cases.
"The Grammar of English Grammars"
Goold Brown
Again: English adjectives, as such, are all indeclinable.
"The Grammar of English Grammars"
Goold Brown
But whenever these words are used adjectively to denote gender, whether we choose to insert the hyphen or not, they are, without question, indeclinable, like other adjectives.
"The Grammar of English Grammars"
Goold Brown