Difficult to find or catch (7)
I believe the answer is:
elusive
'difficult to find or catch' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for elusive that I've seen before include "Transient" , "Slippery, hard to catch" , "Sue about Levi, being shifty" , "Difficult to understand" , "Not easy to pin down" .)