fatten up

fatten up

1. (transitive) To cause to gain weight by means of feeding.

   My cat looks underweight, so I'll fatten him up with higher-calorie cat food.

   I visited my mother for a month, and she managed to fatten me up 20 pounds.

2. (intransitive) To become fat or fatter by gaining weight.
   • 1999, Colm Tóibín, The Blackwater Lightship, New York: Scribner, Chapter 8, p. 246,

     ‘And isn’t Declan looking very thin?’ Madge said. ‘He’ll never get a wife if he doesn’t fatten up a bit.’