Unable to sit still (4)
'unable to sit still' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for antsy that I've seen before include "nervous" , "excited?" , "Eager" .)
(Other definitions for edgy that I've seen before include "Jittery" , "Keyed up" , "ready to flap?" , "Sharp in outline" , "Extremely" .)