Shown key turns (3)
I believe the answer is:
led
'shown' is the definition.
'key turns' is the wordplay.
'key' becomes 'del' (Delete on a keyboard).
'turns' says the letters should be written in reverse.
'del' in reverse letter order is 'LED'.
(Other definitions for led that I've seen before include "Light-emitting diode (abbr.)" , "Went first to show the way" , "Something emitting light" , "induced to" , "had the edge" .)