Entry from British & World English dictionary
The largest of a small group of volcanic islands in the South Atlantic, 2,112 km (1,320 miles) south-west of the British colony of St Helena, of which it is a dependency; population 300 (est. 2006). It was discovered in 1506 by the Portuguese admiral Tristão da Cunha and annexed to Britain in 1816.
Definition of Tristan da Cunha in: