We both thought the best resource was flight, when pursued by so formidable an antagonist; so you will find the nest empty when you call to-morrow.
I had the hint from Holmes that this smooth-faced pawnbroker’s assistant was a formidable man—a man who might play a deep game.
This also was opened, and led down a flight of winding stone steps, which terminated at another formidable gate.
A formidable array of bottles and test-tubes, with the pungent cleanly smell of hydrochloric acid, told me that he had spent his day in the chemical work which was so dear to him.
The swing of his nature took him from extreme languor to devouring energy; and, as I knew well, he was never so truly formidable as when, for days on end, he had been lounging in his armchair amid his improvisations and his black-letter editions.
As to what it was he feared, we can only deduce that by considering the formidable letters which were received by himself and his successors.
There are no more uses of "formidable" in the book.