foothold

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A place providing support for the foot in climbing or standing.
• noun A firm or secure position that provides a base for further advancement.

from The Century Dictionary.

• noun That which sustains the feet firmly and prevents them from slipping; that on which one may stand or tread securely; hence, firm standing; footing; stable position; settlement; establishment.
• noun A kind of light india-rubber overshoe, leaving the heel unprotected; a sandal. Sometimes called tip.

from the GNU version of the Collaborative International Dictionary of English.

• noun A holding with the feet; firm standing; that on which one may tread or rest securely; footing.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun climbing A solid grip with the feet.
• noun military airhead, beachhead, bridgehead, lodgement.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a place providing support for the foot in standing or climbing
• noun an initial accomplishment that opens the way for further developments
• noun an area in hostile territory that has been captured and is held awaiting further troops and supplies