Composer of "The Merry Widow" (5)
I believe the answer is:
lehar
'composer of the merry widow' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lehar that I've seen before include "Operettist" , "Musician" , "Viennese composer" , "He scored" , "Operetta composer" .)