Definition of fattest:
(adj) :
Carrying more fat than usual on one's body; plump; not lean or thin.
(adj) :
Thick; large.
(adj) :
Oily; greasy; unctuous; rich (said of food).
(n) :
(uncountable) A specialized animal tissue with high lipid content, used for long-term storage of energy: fat tissue.
(n) :
(countable) A lipid that is solid at room temperature, which fat tissue contains and which is also found in the blood circulation; sometimes, a refined substance chemically resembling such naturally occurring lipids.
(n) :
(informal, derogatory) A fat person.