Not welcoming one nursed by worried nun - coming to call is cancelled (10)

'cancelled' is the definition.
Both the definition and answer are adjectives. Perhaps they are linked in a way I don't understand?

'not welcoming one nursed by worried nun coming to call' is the wordplay.
I cannot really see how this works, but
'not' could be 'un' (prefix meaning 'not') and 'un' is located in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

'is' acts as a link.

Can you help me to learn more?