In the 13th century when it was first used, fulsome meant simply “abundant or copious.” It later developed additional senses of “offensive, gross” and “disgusting, sickening,” probably by association with foul, and still later a sense of excessiveness: a fulsome disease; a fulsome meal, replete with too much of everything. For some centuries fulsome was used exclusively, or nearly so, with these unfavorable meanings.
Today, both fulsome and fulsomely are also used in senses closer to the original one: The sparse language of the new Prayer Book contrasts with the fulsome language of Cranmer's Book of Common Prayer. Later they discussed the topic more fulsomely. These uses are often criticized on the grounds that fulsome must always retain its connotations of “excessive” or “offensive.” The common phrase fulsome praise is thus sometimes ambiguous in modern use.