key to (something)
1. noun The most important determining factor needed to achieve or accomplish something. The key to writing fiction is to make something that you would want to read. Anything else will just feel insincere. Everyone wants to know the entrepreneur's keys to success.
2. noun That which provides a clearer or more robust understanding of something. This clue could be the key to the criminal's identity. Nuclear scientists are still searching for the key to cold fusion.
3. adjective Having primary importance to ensure the success of something. Strong leadership is key to any successful business. You are key to our plans, Mary. Please, let me know what we can do to convince you to stay with the company.
4. verb To make sure that something matches or is consistent with something else. A noun or pronoun can be used between "key" and "to." If you don't key your expectations to your students' actual abilities, you'll just end up disappointed.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
To make something correspond to something else: I wrote up a teaching guide and keyed it to the materials for each lesson. The worksheets were keyed to the requirements for each course.
The American Heritage® Dictionary of Phrasal Verbs. Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.