fall in

verb

1. To collapse inwards.

   “The heavy rain caused the roof to fall in.”

2. Of a soldier, to get into position in a rank.

   “His men resumed their muskets and fell in.”

3. To come to an end; to terminate; to lapse.

   “On the death of Mr. B., the annuity, which he had so long received, fell in.”

4. To become operative.

   “The reversion, to which he had been nominated twenty years before, fell in.”