monadnock
A hill or mountain standing isolated above a predominantly flat plain.
Eastward from the White Mountains, the open sea of the upland country comes right to the monadnock shore, with hardly an outlying island; southward the upland is covered for miles by an archipelago of monadnock groups and peaks.
Where it comes from
From the name of Mount Monadnock in New England, which derives from an Abenaki word, perhaps menonadenak, menonadenek (“smooth mountain”) or menadenak, menadenek (“isolated mountain”), from aden (“mountain”).
Adapted from the Wiktionary entry monadnock (CC BY-SA 4.0).