(transitive) To cause (a person or animal) to be fat or fatter.
We must fatten the turkey in time for Thanksgiving.
(intransitive, of a person or animal) To become fat or fatter.
He gradually fattened in the five years after getting married.
(transitive) To make thick or thicker (often something containing paper, especially money).
(intransitive) To become thick or thicker.
(transitive) To make (soil) fertile and fruitful.
to fatten land
1612, Joseph Hall, Contemplations vpon the Principall Passages of the Holie Storie, London: Sa. Macham, Volume 1, Book 4, p. 333,
As the riuer of Nilus was to Egypt in steed of heauen to moisten and fatten the earth; so their confidence was more in it then in heauen;