a group of islands 群岛 ■a sea or stretch of water having many islands 多岛屿的海域
语源
early 16th cent.: from Italian arcipelago, from Greek arkhi- 'chief' + pelagos 'sea'. The word was originally used as a proper name (the Archipelago 'the Aegean Sea'): the general sense arose because the Aegean Sea is remarkable for its large numbers of islands