A container partly open (4)

I believe the answer is:

ajar

'partly 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 "not entirely open" , "Part-open" , "partly opened" , "It's nearly open" , "A little bit open, like door" .)

I've seen this clue in The Telegraph.

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