Has one understand one isn't given tick (4,6)

I believe the answer is:

gets across

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'understand one isn't given tick' is the definition.
I can't judge whether this definition defines the answer.

'has one' is the wordplay.
'has' becomes 'gets' ('get' can be a synonym of 'have').
'one' becomes 'across' (I can't justify this - if you can you should give a lot more credence to this answer).
'gets'+'across'='GETS ACROSS'

Can you help me to learn more?

(Another definition for gets across that I've seen is " Manages to communicate".)

I've seen this clue in the Evening Standard.

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