flab vs fatty tissue

flab and fatty tissue both are nouns.

Word	Noun	Adjective	Verb	Adverb
flab	Yes	No	No	No
fatty tissue	Yes	No	No	No

As nouns, fatty tissue is a hypernym of flab; that is, fatty tissue is a word with a broader meaning than flab:

flab: loose or flaccid body fat
fatty tissue: a kind of body tissue containing stored fat that serves as a source of energy; it also cushions and insulates vital organs

Other hypernyms of flab include adipose tissue, fat.

flab (noun)	fatty tissue (noun)
loose or flaccid body fat	a kind of body tissue containing stored fat that serves as a source of energy; it also cushions and insulates vital organs