Excessively flattering, complimentary, or enthusiastic in a way that seems insincere or overdone.
From Middle English, combining full with -some (meaning full of). Originally it just meant 'full' or 'abundant,' but by the 16th century it developed the negative sense of 'excessively full' or insincere praise.
Fulsome praise is the worst kind of compliment—it's so over-the-top that it makes you suspicious of the person's motives, which is why this word went from neutral to negative over time.
Complete word intelligence in one call. Free tier — 50 lookups/day.