Stare at (7)
I believe the answer is:
eyeball
'stare at' is the definition.
(to eyeball something is to stare at it)
This is all the clue.
(Other definitions for eyeball that I've seen before include "Look at closely" , "One of two in confrontation" , "Spherical optical organ" , "One faces one in confrontation" , "Look confrontationally" .)