peninsula

Concise Oxford English Dictionary © 2008 Oxford University Press:
peninsula /pɪˈnɪnsjʊlə/

▶noun a long, narrow piece of land projecting out into a sea or lake.

– derivatives
peninsular adjective.

– origin C16: from L. paeninsula, from paene ‘almost’ + insula ‘island’.

usage: Do not confuse the spellings peninsula and peninsular. Peninsula is a noun (the end of the Cape Peninsula), whereas peninsular is the adjectival form (the peninsular part of Malaysia).