Looked hard (6)
I believe the answer is:
stared
'looked hard' is the definition.
(to stare is to look hard at something)
This is the entire clue.
(Other definitions for stared that I've seen before include "Looked with a fixed gaze" , "Looked at long and fixedly" , "Subjected to prolonged gaze" , "Gaped" , "Looked hard and fixedly" .)