The word “fulsome” presents a problem that usage and etymology fail to sort out. It either means “abundant,” “offensive” or, perhaps as a compromise, “offensively abundant.”
Dictionaries usually give at least the first two meanings while most usage guides insist on the third. The Associated Press Stylebook says “it means disgustingly excessive” and should not be used to mean “lavish or profuse.” The BBC News Styleguide says, probably incorrectly, that “fulsome is not a close relative of full, and does not mean generous.”
The word might have derived from the word “foul,” giving the “offensive” meaning credence. But the Oxford English Dictionary and others suggest it comes from “full.” The OED’s corpus has a century of examples where the word meant “abundance” before examples where “excessive” or “foul” came into play.
The negative sense seems to have surpassed the positive sense centuries ago, although in recent usage the positive sense seems to predominate. According to the Online Etymology Dictionary, “since the 1960s, however, it commonly has been used in its original, favorable sense, especially in ‘fulsome praise.'”