Sly to reach out pointlessly (4)
I believe the answer is:
arch
'sly' is the definition.
(thesaurus)
I can't explain the rest of the clue.
(Other definitions for arch that I've seen before include "Curved vault" , "Roguish - superior" , "Mischievous - curve" , "Chief - opening with curved top" , "This enemy is major" .)