thinking cap

Probably by analogy with considering cap, which is attested from the early 17th century.[1]

• (Received Pronunciation, General American) IPA^(key): /ˈθɪŋkɪŋ ˌkæp/
• Hyphenation: think‧ing cap

thinking cap (plural thinking caps)

1. (humorous) A metaphorical piece of headgear supposedly worn by a person to assist them in thinking about how to solve a problem.

   This project looks like it will be a real challenge – put on your thinking cap!

   • 1855 February 28, “On with Your Thinking-caps!”, in Youth’s Penny Gazette, volume XIII, number 5 (number 317 overall), Philadelphia, Pa., New York, N.Y., Boston, Mass.: American Sunday-School Union, →OCLC, page 18, column 1:

     Now suppose they put on their "thinking-caps" a moment or two, and consider what is going on in the great world around them. [...] Before you pull off your "thinking-cap" cast a look around your own country—free, prosperous, powerful, independent; yet how full of wickedness, and how unmindful of its obligation to the God of nations!

   • 1862 April, “Putting on the Thinking Caps”, in The Student and Schoolmate, and Forrester’s Boys and Girls Magazine, volume XL, number IV, Boston, Mass.: Galen James and Company, […], →OCLC, page 109:

     Come children, gather around the desk, and we will have a chat for half an hour. We want you to put on your thinking caps, and show what manner of boys and girls you are.

   • 1864, William M. Thayer, “Introduction”, in A Child’s History of the Rebellion, from the Bombardment of Fort Sumter to the Capture of Roanoke Island, Boston, Mass.: Walker, Wise, and Company, […], →OCLC, page 24:

     The story you shall have, then, just as well as I can tell it: and you must put on your thinking-caps, so as to remember all you can of it; and be sure to ask questions about what you don't understand.

   • 1873 October 11, “Jessie’s Token of Love”, in The Temperance Record: The Organ of the National Temperance League, number 914, London: Published for the National Temperance League by William Tweedie, […], →OCLC, page 485, column 2:

     "Costly gifts, my dear child, are not always acceptable as a proof of love. And if you put on your thinking cap, perhaps you will find that you, too, can take an acceptable keepsake to your teacher." / "Why, I'm sure I've nothing worth taking to her, mamma. And all the thinking caps in the world can't help me to an idea."

   • 1916, Sara H. Merrill, “The Hero Turtle”, in John Martin [pseudonym; Morgan van Roorbach Shepard], editor, John Martin’s Annual: A Jolly Big Book for Little Folks, Garden City, N.Y.: Published by John Martin’s House Inc. […] for Platt & Peck Co., →OCLC:

     As time passed the Great Spirit grew fonder and fonder of his good-natured friend, and was grieved to see him suffer for the lack of a full dinner pot and stomach, so the Great Spirit put on his thinking-cap and learned a way to help Mr. Turtle. "The old fellow needs a wife!" said the Great Spirit taking off his thinking-cap.

   • 1989 February 23, Molly Burney (witness), Hearing on the Reauthorization of VISTA: Hearing before the Subcommittee on Select Education of the Committee on Education and Labor, House of Representatives, One Hundred First Congress, First Session: […] (serial no. 101-5), Washington, D.C.: U.S. Government Printing Office, →OCLC, page 60:

     There are two of us with children and just think now, if two of us with children can do this, just think what the young people who don't have children, coming out of school, can do if they put their thinking caps on and just volunteered and sat down and talked to find out what they can do. I know there are a lot of them out there can do it.

   • 2004, Evan Morris, “Food and Drink”, in From Altoids to Zima: The Surprising Stories behind 125 Brand Names, New York, N.Y.: Fireside, Simon & Schuster, →ISBN, page 70:

     So Reuben [Mattus] put on his thinking cap and came up with the name Häagen-Dazs for his new line of premium, high-fat ice cream. Although it sports an umlaut and sounds Scandinavian, the name Häagen-Dazs is pure nonsense—it doesn't actually mean anything in any known language.

   • 2013, James A. Bellanca, “Toward More Systematic Searches”, in The Focus Factor: 8 Essential Twenty-first Century Thinking Skills for Deeper Student Learning, New York, N.Y.: Teachers College Press, →ISBN, page 70:

     [I]f he stopped, took a deep breath, and put on a thinking cap to make a plan, he would have a greater chance of finding the object and finding it sooner.

• thinking-cap

• “thinking cap, n.” under “thinking, n.”, in OED Online ⁠, Oxford, Oxfordshire: Oxford University Press, September 2009.
• “thinking cap, n.”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.