Pointed mention of pie in the sky (5)
I believe the answer is:
spiky
'pointed' is the definition.
(thesaurus)
'mention of pie in the sky' is the wordplay.
'mention of pie' becomes 'pi' (I am not sure about this - if you are sure you should believe this answer much more).
'in the' is an insertion indicator.
'pi' going within 'sky' is 'SPIKY'.
Can you help me to learn more?
(Other definitions for spiky that I've seen before include "Having sharp prongs" , "having ears" .)