Chappaquiddick Island (CHAP-uh-KWID-dik), part of Edgartown, Dukes co., SE Mass., off E Marthas Vineyard, from which a narrow channel separates it; c.5 mi/8 km long. Resort area. Cape Poge (lighthouse here), at N tip, extends N into Nantucket Sound. Wasque Point at S tip; has lighthouse (41°25'N 70°27'W); site of famous Dyke Bridge.