Language can be a slippery beast, with the meanings of words changing over time. This can be a great source of confusion, especially if a word ends up with two distinct, even contradictory meanings. One example of this occurs with the word fulsome.
Fulsome now has two separate meanings and it isn’t always clear which meaning a writer intended. The original sense of the word, from as far back as 1250 according to the Oxford English Dictionary, was, simply, “abundance”. To give fulsome praise was to praise lavishly.
Some time after this the word began to take on a more negative sense of excess. It came to mean “obnoxiously full” rather than just full. To give fulsome praise now meant to give insincere or exaggerated praise.
More recently, the word has gone full circle and become more widely used in its original sense : abundant without any negative connotation. People describe praise as “fulsome” and imply no criticism. The problem is that the intended meaning of “fulsome apology” or “fulsome praise” isn’t clear. The word may be being used in a complimentary sense, or in an insulting one.
The Oxford Dictionary maintains that the negative sense of the word is the correct one. It says :
Although the earliest sense of fulsome was ‘abundant’, this is now regarded by many as incorrect; the correct meaning today is said to be ‘excessively flattering’. This gives rise to ambiguity: the possibility that while for one speaker fulsome praise will be a genuine compliment, for others it will be interpreted as an insult.
However, this seems out of step with much common usage. To avoid the ambiguity, perhaps the best approach is to avoid the word altogether and find a clearer alternative. If you choose to use it, be aware of the ambiguity.