Definition of "fatten"
fatten
verb
third-person singular simple present fattens, present participle fattening, simple past and past participle fattened
(transitive) To cause (a person or animal) to be fat or fatter.
Quotations
And if the mat[t]er be too little, the vertue of digestion fayleth, and the bodye is dryed, and if the matter and meate be moderate, the meats is well digested, and the bodye fattened, the heart comforted, kinde heate made more, the humors made temperate, & wit made cleere:
1582, Stephen Batman, transl., Batman vppon Bartholome his Booke De Proprietatibus Rerum, London: Thomas East, Book 6, Chapter 25, p. 82
In that classroom full of oily potato-chip-fattened adolescents, she was everyone’s ideal of translucent perfume-advertisement femininity.
1969, Margaret Atwood, The Edible Woman, Toronto: McClelland & Stewart, published 2010, Part 1, Chapter 4
(transitive) To make thick or thicker (something containing paper, often money).
Quotations
It was the impotence of the money, and of all the pent-up warlike fancies that had earned it, to do anything but elaborate the wardrobe and fatten the financial portfolios of the owners of Empire Comics that so frustrated and enraged him.
2000, Michael Chabon, The Amazing Adventures of Kavalier and Clay, New York: Random House, Part 3, Chapter 2, p. 177
(intransitive) To become thick or thicker.
Quotations
A broad river of white paper rushed constantly up from the cylinder and leaped into a mangling chaos of machinery whence it emerged a second later, cut, printed, folded and stacked, sliding along a board with a hundred others in a fattening sheaf.
1929, Thomas Wolfe, Look Homeward, Angel, London: Heinemann, published 1930, Part 2, Chapter 22