Green’s Dictionary of Slang

connection n.

also connect, connexion
[connect v.]
[1920s+]

1. (orig. US) a supplier of contraband liquor.

2. (orig. US, also nec) a supplier of drugs; esp. a wholesaler (rather than a street seller).

3. (orig. US) the act of contacting a drug dealer; thus connection dough, money for drugs.

4. (orig. US) the person with whom one achieves sexual fulfilment; thus the act itself.

5. (orig. US) any form of connection or go-between, e.g. one who helps with a crime.

6. (US prison) a corrupt guard, or trusted prisoner, who helps inmates smuggle contraband into and within prison.

In phrases

house connect (n.)

[1990s+] (US drugs) a drug dealer who works from their home, rather than the street.