1
general::
Search for, seek to discover, as in He was trying to root out the reason for her long absence. This idiom alludes to the way hogs dig by using their snouts. [Mid-1800s]
American Heritage Idioms
2
general::
Phrase(s): root something out
to get rid of something completely; to destroy something to its roots or core. • No government will ever root out crime completely. • The principal wants to root out troublemakers at the local school.
McGrawhill's American Idioms And Phrasal Verbs