Trust to assume nurses record finish (6,4)

I believe the answer is:

depend upon

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'trust' is the definition.
Although both the answer and definition are verbs in their base form, I can't see how one could define the other.

'assume nurses record finish' is the wordplay.
'assume' becomes 'don' (I've seen this before).
'nurses' is an insertion indicator (nurse can mean to hold onto or harbour).
'record' becomes 'ep'.
'finish' becomes 'endup' (synonyms).
'ep'+'endup'='ependup'
'don' going around 'ependup' is 'DEPEND UPON'.

'to' is the link.

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