keep under

verb

to remain or cause to remain below (a surface)
(tr, adverb) to cause to remain unconscious
(tr, adverb) to hold in submission

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012