From WordNet (r) 3.0 (2006) [wn]:
mainland
n 1: the main land mass of a country or continent; as
distinguished from an island or peninsula
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Mainland \Main"land`\, n.
The continent; the principal land; -- opposed to island, or
peninsula. --Dryden.
[1913 Webster]
After the two wayfarers had crossed from the peninsula
to the mainland. --Hawthorne.
[1913 Webster]