Do library research (4)
I believe the answer is:
read
'do library research' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for read that I've seen before include "what follows 18 [OMASUM] in a 17 [RUMINANT]" , "Use a book" , "Con" , "Interpret writing" , "See - peruse - understand" .)