The best replacement for an island is continent.

The best alternatives to an island are rated as following:
★★★★★  continent
★★  peninsula
★  on an island
  in an island

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Speaking about an island, one probably shouldn't forget about lake.

Other search terms related to an island and their ratings are:
★★★★★ lake
You have in mind a companion for an island and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of an island in all years. Click on graph for more.
an island
continent
peninsula