What's the "een" in Halloween?
1620s; implied earlier as a past participle adjective (early 15c.), from Latin corrugatus, past participle of corrugare "to wrinkle very much," from com-, intensive prefix (see com-), + rugare "to wrinkle," of unknown origin.
corrugator cor·ru·ga·tor (kôr'ə-gā'tər)
A muscle that draws the skin together, causing it to wrinkle.