Other forms: fats, fatter, fattest
Fat means having a heavy, round body, and it is the plain word. It is also the substance itself — the fat on meat, fat in the frying pan, body fat — and there it is entirely neutral and used constantly in cooking and nutrition.
Applied to a person, the word is blunt and often rude, and English has built a whole ladder of softer options: overweight is clinical, large and big are polite, plus-size is commercial, and heavy is gentle. Which of them is acceptable changes by decade and by country, so a learner is safest describing a person as overweight and reserving fat for food. The adjective also means thick or large in a neutral way: a fat book, a fat cheque, fat chance — which sarcastically means no chance at all.
1adjectivefatHaving a heavy, round body.~13%
“The cat is fat and entirely unrepentant.”
2noungreasyThe greasy substance in animal bodies and in food.~75%
“Cut the fat off before you grill it.”
3adjectivethickThick or large.~12%
“She was carrying a fat envelope of papers.”
Shares are an estimate: a language model read 11 sentences found in the wild and placed 8 of them on a sense (3 were unclear) — a count of our sample, not a measurement of English.
fat is a body shape, or a substance.
Also accepted in games: overweight
Old English faett was the past participle of a verb meaning to fatten, so fat originally meant fattened — something that had been made fat, usually deliberately, usually an animal. The adjective describing a person is a later loosening.
Proto-Indo-European
*peyH-
Proto-West Germanic
*faitid — fatted
Old English
fǣtt — fatted, fat
Middle English
fat
English, today
fat
Built from
From Middle English fat, from Old English fǣtt (“fatted, fat”), from Proto-West Germanic faitid (“fatted”), originally the past participle of the verb faitijan (“to make fat”), from fait (“fat”).
Etymology from Wiktionary, CC BY-SA