?Ful? is the Anglo-Saxon fl (foulness), not ful (full); ?some? is the affix meaning united with, the basis of something; as, gladsome, mettlesome, gamesome, lightsome, frolicsome, etc., etc.
?No adulation was too fulsome for her [Elizabeth], no flattery of her beauty too great.? ?Green: Short History of England, chap. viii. sec. 3, p. 376.