Another set of words involves the suffix “-ful,” which derives from Anglo Saxon, and “-ous,” which derives from old French by way of Latin. The both mean “full of” whatever is the root to which it attaches ("harmonious, full of harmony"). We have a small group of words which can take either suffix and mean essentially the same thing: beautiful and beauteous, wonderful and wondrous, plentiful and plenteous, graceful and gracious, pitiful and piteous, bountiful and bounteous, joyful and joyous, rightful and righteous, doubtful and dubious. All of these pairs are nearly synonymous, but not quite. Each one has taken on slightly different hues and one almost has to consult a dictionary to see the proper usage for each. The best example might be graceful and gracious. “Graceful” suggests beauty of form, expression, or movement, especially physical movement. “Gracious” suggests a person showing kindness or courtesy, mercy or compassion. Both describe people who are full of grace, but one a physical grace, the other a mental grace.
But we also have many words ending in “–ful” that don’t have a near synonym ending in “-ous” and many ending in “-ous” that don’t have a brotherly “-ful.” Many of them should, though, with some fanciful (fancifous) or humorous (humorful) results. For example, “sinful” might have “sinuous,” the one meaning full of sin, the other meaning full of twists and turns, like the serpent that tempted Adam and Eve with that tasty, sinful (sinuous) apple. If there’s a “righteous,” why not a “wrongeous?” For every “sorrowful,” there should be a “sorrowous,” a “hateous” for every “hateful,” a “stupendeful” for every “stupendous,” a “malodorful” for every “malodorous,” a “ridicuful” for every “ridiculous.” And to end this discussion, we should have both a “bsifous” as well as a “bsiful.”