[UNDER-1 5 c.] An undercurrent; fig. a tendency beneath the surface of things.

1

1849.  Cupples, Green Hand, xiv. Either she [the ship] stood still, or she’d caught some eddy or under-drift.

2

1891.  Daily News, 12 Jan., 215. Thus the underdrift of things is in favour of an easier money market.

3