Tall concert instrument (4)
I believe the answer is:
harp
'tall concert instrument' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for harp that I've seen before include "Emblem of Ireland" , "Chordophone" , "''The ... that once through Tara's halls'' (4)" , "Keep on about" , "Lyre" .)