fatted

kill the fatted calf produce a lavish celebratory feast.

☞ The allusion is to the New Testament story of the prodigal son (Luke 15:11–32), in which the forgiving father orders his best calf to be killed in order to provide a feast to celebrate the return of his wayward son. Fatted is an archaic form of the verb fat meaning 'make or become fat'. Nowadays we use the forms fatten and fattened.