Agreement uniting Pennsylvania and Connecticut (4)
I believe the answer is:
pact
'agreement' is the definition.
(a pact is an agreement or deal)
'pennsylvania and connecticut' is the wordplay.
'pennsylvania' becomes 'PA'.
'and' means one lot of letters go next to another.
'connecticut' becomes 'CT' (US postal abbreviation).
'pa'+'ct'='PACT'
'uniting' is the link.
This may not be correct. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for pact that I've seen before include "Agreement, bargain" , "deal" , "Settlement" , "Alliance" , "International treaty" .)