A glass container left open? (4)
I believe the answer is:
ajar
'left open?' is the definition.
(I've seen this before)
'a glass container' is the wordplay.
'glass container' becomes 'jar' (I've seen this before).
'a'+'jar'='AJAR'
(Other definitions for ajar that I've seen before include "near closing?" , "Half-closed" , "It's nearly open" , "Half-open" , "A little bit open, like door" .)