Pa expanded (12)

I believe the answer is:

pennsylvania

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'pa' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for pennsylvania that I've seen before include "State of NE? USA" , "State of NE US" , "State of northeastern US" .)

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