A setter is showing intent (3)
I believe the answer is:
aim
'intent' is the definition.
(synonyms)
'a setter is' is the wordplay.
'setter is' becomes 'im' (the setter is the person who set the crossword).
'a'+'im'='AIM'
'showing' is the link.
(Other definitions for aim that I've seen before include "Train" , "Purpose, intention" , "Direct, intend" , "Aspire" , "Point (a camera)" .)