Piece taken dal segno maestro turned in (5)
I believe the answer is:
among
'in' is the definition.
(in amongst something)
'piece taken dal segno maestro turned' is the wordplay.
'piece taken' indicates a hidden word.
'turned' says the letters should be written in reverse.
'gnoma' is hidden in the letters of 'dal segno maestro'.
'gnoma' written backwards gives 'AMONG'.
(Other definitions for among that I've seen before include "In the middle of, say a crowd" , "Go man! (anag.)" , "Included with - inside" , "when in company" , "Together with" .)