A container not quite closed (4)
I believe the answer is:
ajar
'not quite closed' is the definition.
(I've seen this in another clue)
'a container' is the wordplay.
'container' becomes 'jar' (jar is a kind of container).
'a'+'jar'='AJAR'
(Other definitions for ajar that I've seen before include "Barely open" , "Half-open" , "It's nearly open" , "Left open" , "Not quite closed" .)