Just open a container (4)

I believe the answer is:

ajar

'just open' is the definition.
(I've seen this before)

'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 "Half-closed" , "letting in a little light?" , "It's nearly open" , "Barely open" , "opened tentatively?" .)

I've seen this clue in The Times and The Sun.

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