Main Entry: fall in

Function: intransitive verb

Date: 1719

1 : to sink inward <the roof fell in>
2 : to take one's proper place in a military formation

— fall in with 1 : to concur with <had to fall in with her wishes>
2 : to harmonize with <it falls in exactly with my views>
3 : to begin associating with <she fell in with a bad crowd>