fortunate discovery (11)
I believe the answer is:
serendipity
'fortunate discovery' is the definition.
'serendipity' can be an answer for 'discovery' (thesaurus). I also know that 'fortunate' relates to this answer.
This is all the clue.
(Other definitions for serendipity that I've seen before include "Faculty of making beneficial discoveries by accident" , "Fortunate happenstance" , "Beneficial happenstance" , "Fortunate chance" , "The accidental discovery of good fortune" .)