With cap still on, screwing one end up? (8)
I believe the answer is:
unopened
'with cap still on' is the definition.
(eg a bottle with its cap still on)
'screwing one end up?' is the wordplay.
'screwing' indicates an anagram.
'one'+'end'+'up'='oneendup'
'oneendup' with letters rearranged gives 'UNOPENED'.
(Other definitions for unopened that I've seen before include "Remaining sealed" , "shut" , "Still sealed as post may be" , "barred" , "Remaining closed" .)