tubby vs fat

tubby is not a noun while fat is a noun.

Word	Noun	Adjective	Verb	Adverb
tubby	No	Yes	No	No
fat	Yes	Yes	Yes	No

tubby (noun)	fat (noun)
	excess bodily weight
	a kind of body tissue containing stored fat that serves as a source of energy; it also cushions and insulates vital organs
	a soft greasy substance occurring in organic tissue and consisting of a mixture of lipids (mostly triglycerides)

tubby (adjective)	fat (adjective)
short and plump	having an (over)abundance of flesh
	containing or composed of fat
	marked by great fruitfulness
	lucrative
	having a relatively large diameter

tubby (verb)	fat (verb)
	make fat or plump