archaic : FRIGHTFUL, LOATHSOME
Etymology: Middle English, from uggen to fear, inspire fear, from Old Norse ugga to fear--The American Heritage Dictionary of the English Language, Fourth Edition. New York: Houghton Mifflin, 2000.
I agree with J. N. Hook that ugsome is "an archaic word worth reviving.
It means horrid, loathsome, filling with dread, uglier than ugly: 'a scowling, ugsome man, with scar from cheek to jaw'" (65).--The Grand Panjandrum. New York: Collier, 1991.
The concinnity of sounds in ugsome--with the low, gutteral vowel of "ugh," repeated with a quick report in the syllable "some," intensifies the presence of (the effect of) the word's presence, trumping (or "out-trumpeting") the sweet "e" sound trailing "ugh" in ugly.
"Ugsome" is also a welcome, long-absent completion of the apt antithetical pair of "ugsome" v. "handsome." "Ugly" does not have a fitting sonic antithesis: there is no such word as "handly." With "handsome" in wide, active play, it is surprising that the desire for order within the mind has not noted the absence of handsome's fitting opposite and embraced, so to speak, the orphan ugsome.