It’s an adjective that describes individuals who put their faith in someone else's views.
It rather looks like the sort of word somebody has forged in a fit of misplaced inventiveness. It was created by Sir Thomas Urquhart in 1652 in a book with a Greek title I won’t try to reproduce but which has the subtitle The Discovery of a Most Exquisite Jewel. He took it from the church Latin fides implicita, implicit faith.
He used it as a scathing epithet for academic types, gown-men, who were very happy to believe the assertions of their predecessors and were prepared to take all things literally on trust and without examination. So far as anybody knows, Sir Thomas was the only person who ever used it. It did appear in an issue of Blackwood’s Edinburgh Magazine in 1817, but in a caricature of Sir Thomas that had him refer to “those shallow and fidimplicitary coxcombs, who fill our too credulous ears with their quisquiliary deblaterations”.
Those are a nice pair of knock-down words, as Humpty Dumpty might have said to Alice. Quisquiliary is Urquhart’s variation on quisquilian, meaning worthless or trivial; deblateration comes from the Latin deblaterare, to prate or blab out.
These old-timers certainly knew how to insult people. We’ve largely lost the art of elaborate epithetical impugnment, relying more on crude invective these days. Polysyllabic scurrility should be our watchword!