Doubty

That treated well, of a full noble story Of the doubty waye, to the tower perillous Howe a noble knight, shoulde winne the victory Of many a serpent, fowle and odious

Source: wiktionary

he thereto aimed, namely, to be a most doubty and hardy warrior, an excellent orator, a right valiant captaine and commander

Source: wiktionary

So, stout, hardy, valiant, doubty, couragious, adventurous, all comprehended under the Latin word (fortis).

Source: wiktionary