Heavy is a synonym of burdensome.
As adjectives the difference between heavy and burdensome
is that
heavy is (of a physical object) having great weight or
heavy can be having the heaves while
burdensome is of or like a burden; arduous or demanding.
As an adverb heavy
is heavily.
As a noun heavy
is a villain or bad guy; the one responsible for evil or aggressive acts.
As a verb heavy
is to make heavier.