Extremely precise (4)
I believe the answer is:
very
I believe this clue is a double definition.
'extremely' is the first definition.
(very can mean extremely or considerably)
'precise' is the second definition.
(similar in meaning)
(Other definitions for very that I've seen before include "Exactly, really" , "Kind of light" , "Actual; in a high degree" , "To a large extent" , "Sort of light" .)