apron string

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

• noun The string of an apron. Usually used in the plural with tied to indicate complete control or dominance.

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

• The string of an apron.
• to be unduly controlled by a wife or mother.

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

• noun One of the pair of strings or narrow sewn cloth strips used to fasten an apron around the wearer's waist.
• noun idiomatic, usually pluralized A symbol of the domestic ties binding a male to a female (as a husband to a wife or a son to a mother).

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

• noun (usually used in the plural) a cord used to tie an apron at the waist